New Left Review at 50: no balloons, of course, and definitely no party games. The very idea of "celebration" smacks of consumerist pseudo-optimism. Mere chronology is, after all, an untheorised concept. We should see it as not so much an ­anniversary, more an over-determined conjuncture.

It is hard not to be intimidated by New Left Review. At times, the journal can seem like an elaborate contrivance for making us feel inadequate. One's relation to it conjugates as an irregular verb: I wish I knew more about industrialisation in China; you ought to have a better grasp of Brenner's analysis of global turbulence; he, she, or it needs to understand the significance of community-based activism in Latin America. For many Guardian readers (and others), the journal functions like a kind of older brother whom we look up to – more serious, better informed, better travelled, stronger, irreplaceable. Well, maybe a tiny bit solemn at times (we could draw lots for who gets the job of telling Perry Anderson to lighten up), and perhaps when we were out of touch for longish stretches, life seemed a bit easier. But then we meet up and it's a case of respect at first sight, all over again.

It hasn't always been like this: even older brothers had rocky periods in their youth – misguided enthusiasms, failed relationships, moody withdrawals. Some readers may remember times when NLR seemed hell-bent on sectarian purism, theoretical slavishness and a wilful opacity. It has been through several changes of identity in the past 50 years, and memories of some of these earlier phases may hamper the efforts that it has made recently to reach out to a more diverse readership. But there is a lot in that history to be proud of. The journal has, in its own unbending fashion, registered and responded to huge changes in the world during this half-century, and in doing so has made a stock of ideas available well beyond the ranks of those who may at any point have shared its particular form, or forms, of Marxism (an allegiance that has itself modulated, perhaps even attenuated somewhat, over the decades). Some things about the journal, however, don't change. What other publication would take out a full-page advertisement in a national newspaper announcing its "quinquagenary issue"? NLR has been accused of many things, but never of populist dumbing-down.

The biography of the review cannot be reduced to a formula: its experience so far has been too rich and too contradictory. But it would be fair to say that a journal that began life hoping to animate and express organised popular movements on the left soon became a more emphatically theoretical enterprise, albeit with certain Leninist or Trotskyist longings held in reserve. Then, in the 1980s, it began to interpret its intellectual task in more expansive terms, and since 2000 it has been self-consciously a "journal of ideas" – on the left, to be sure, but distant from radical movements in the present or any worked-out political blueprint for the future.

As a severely intellectual journal committed, in principle, to the radical transformation of society, NLR had few models to draw on in British history – and the journal grew out of and was for a long time rooted in British culture, however internationalist it has since become. There had been a lot of small, usually transient, journals of the left, such as William Morris's Commonweal (1885-90) or the original Left Review (1934-38); there were political periodicals closer to the parliamentary fray, such as the New Statesman (1913- ) or Tribune (1937- ); and there had been more eclectic, radical-leaning reviews of art, culture and politics, such as the New Age (1907-22). But to find another successful journal of ideas conducted at the highest intellectual level by a self-consciously radical group we may have to go back to the Westminster Review, the journal of the Philosophic Radicals of the early 19th century. In the present, the publication closest in spirit, despite all the obvious differences of form, may be the London ­Review of Books (there is some overlap in contributors), but NLR is less literary, even more political, and committed to more systematic economic analysis and theoretical construction. It also concerns itself very little with British politics and culture these days.

In so far as there was a conscious model in the early years, it was Sartre's Les Temps Modernes, and an idealised version of Parisian intellectual life in the 1950s seems to have retained something of a hold over several of the review's leading spirits. It takes quintessential black-polo-neck subjects such as philosophy and film very seriously indeed; other art forms, and more or less all of popular culture, come a long, long way behind. Although there have been periodic shake-ups of the editorial board, complete with affirmations of the need to bring in new blood, the core group are now all around 70 and so date their formation to those heady days of bringing the news from Paris in the decade from 1958 to 1968.

The 50th-anniversary issue includes articles by several of the NLR's long-serving stalwarts – Tariq Ali, Perry Anderson, Robin Blackburn, Mike Davis – as well as interviews or reprinted pieces by noted figures of the intellectual left such as Eric Hobsbawm and Stuart Hall. These names signify a quite striking element of continuity. Anderson and Blackburn were at the head of the younger group who took over direction of the journal in 1962, after two years of Hall's editorship, and they, together with Ali, Davis and a handful of others, have been constant or recurrent members of the editorial board since the 1960s. Anderson was nominally the editor from 1962-83 (the journal has always emphasised its collective ethos, and from the outside it has not been clear how responsibility has been divided between editor and editorial board); Blackburn then took over until the end of 1999, at which point a new series of the journal was relaunched, initially under Anderson's editorship once more; Susan Watkins has been the editor since 2003. Exact circulation figures have always been hard to come by, as has any reliable information about its inner workings, but its bi-monthly issues are said currently to sell around 10,000 each. Although Anderson family money is rumoured to have bailed out the journal in the early 1960s, it has long been self-financing, without grants or subsidies, and over the past five years has even made a modest profit.

But these continuities of personnel mask some dramatic shifts of direction and changes in character. The review was founded in 1960 out of a merger of two existing journals, Universities and Left Review and the New Reasoner, the former representing an upsurge of political and cultural radicalism in the late 1950s, especially strong in universities, that repudiated the reformism of the Labour party, while the latter provided a rallying ground for those communists and ex-communists who, post-1956, disowned orthodox Stalinism. New Left clubs were formed around the country, and the Campaign for Nuclear Disarmament provided a mobilising and unifying focus. For a brief period, the review was part of a wider movement. But after the 1962 changeover, it focused more exclusively on preparing the theoretical ground for "revolution" (it can be hard now to remember what an everyday term "revolution" was in the 1960s and 1970s). One of the NLR's most notable services was in importing and disseminating European ideas, especially the rich tradition of Hegelianised Marxisms, but also other styles of work in, for example, sociology and psychoanalysis. In 1970 a publishing house was set up – New Left Books, which mutated into Verso – and this helped to make many classic works of European social thought available in English at a time when the expanding system of higher education was hungry for such texts. Established socialist thinkers such as Isaac Deutscher and Raymond Williams were important to the review in its early years; for a while the example of the Belgian Trotskyist economist Ernest Mandel was influential; at various points there was particularly sustained engagement with the ideas of Antonio Gramsci and Louis Althusser.

In the course of the 1980s, the political imagination of the left had to be re-fashioned to acknowledge the dramatic transformations of that decade, including the end of "actually existing socialism". This and the following decade saw ructions and resignations at the review itself, as well as attempts to remedy its comparative neglect of now prominent issues such as feminism and the environment. Its denunciation of "the American empire", especially through the so-called humanitarian wars of the 1990s, was one constant; its attempts to uncover the global operation of the new forms of capitalism were another. But questions about what it now meant to be committed to "a socialist future" became more insistent and invited a more fundamental rethinking of the function of the journal itself. NLR 238, published at the end of 1999, was to be the last of the original series.

The first issue of the new series appeared at the beginning of 2000, with a dramatically improved layout and appearance (high-minded left asceticism had tended to favour journals that looked like cyclostyled parish magazines), a regular book review section and signed editorials. The first of these consisted of a stern, unsparing assessment by Anderson of the challenges facing the left at the start of the new century. Some readers were shocked by its Olympian bleakness. "The only starting point for a realistic left today is a lucid registration of historical defeat." (I can't help admiring the sentence as well as the sentiment here, especially that last phrase with its indomitable commitment to lucidity about the wreck of one's dreams.) Anderson found "neoliberalism" triumphant across the globe: no effective countervailing radical force existed. But that, it was implied, is all the more reason to seek a properly explanatory understanding of the forces at work in the world today. Only on that basis – a systematic, deeply informed, international analysis – could even the most tentative steps be taken towards formulating a viable alternative. The message may have been bleak, but the tone was resolute: the guiding principle for the review should be "the refusal of any accommodation with the ruling system, as of any understatement of its power".

Over the years, NLR had shown a proper regard for Gramsci's celebrated motto "pessimism of the intellect, optimism of the will", but many readers thought Anderson's 2000 editorial overdid the pessimism and gave precious little nourishment to the optimism. A French critic, in a reproach that must have stung the famously nonparochial and francophile Anderson, accused him of viewing things too narrowly from one side of la Manche: various forms of resistance, it was suggested, were much more visible in France, while others felt that forms of protest elsewhere in the world were similarly being undervalued. But, a decade on, Anderson's pessimism on this score scarcely seems exaggerated: in so far as the imperium of neoliberalism is being curbed, which is not far, it does not appear to be primarily the outcome of organised and politically effective opposition.

Anderson also announced another kind of change in the character of the journal, which was henceforth to be open to a greater variety of voices. Again, there were murmurs about betrayal and elitism – NLR as a virtual club for global intellectuals rather than a getting-its-hands-dirty helper in local struggles – but perhaps such objections mistake what a progressive journal of ideas can and should do. Personally, as a relative outsider to this milieu, I much prefer the hospitable pessimism of the current NLR to the excluding optimism of its more sectarian days. But there's no doubt that its present character raises again the question of what a journal of "the left" should be aiming at when it is not in constructive relations with any organised radical or progressive movements beyond its pages.

Now, in this anniversary issue, the editorial by Susan Watkins takes stock once more. Attention focuses on the financial crash of 2008 and on the banks' subsequent recovery. The former might have seemed to offer the left some hope: the "system" was imploding, as in Marxist or post-Marxist theory it was meant to do. Those famous "contradictions of capitalism" were coming home to roost. Except, as Watkins coolly insists, they haven't; so far there has been adjustment rather than apocalypse. Moreover, this convulsion of the world's financial system seems to have generated precious little political turmoil or popular insurgency. In one of those steely sentences that the modern NLR is so good at, she writes: "That neoliberalism's crisis should be so eerily non-agonistic, in contrast to the bitter battles over its installation, is a sobering measure of its triumph."

So what is there left to do – and what is there to do that is left? Plenty, it turns out. There may be no "immediate practical project", so the concern has to be with the longue durée. "To attend to the development of actually existing capitalism remains a first duty for a journal like NLR." Or again: "A priority for the Review in the coming years should be a new typology of development outcomes in the age of global finance. Another is a map of the global proletariat – locations, sectors, differentials – alive to contemporary makings and unmakings of class."

To some, this may seem like little more than keeping that "registration of defeat" up to date, but the commitment to information and understanding seems admirable to me. In the final paragraph of her editorial, Watkins appears momentarily tempted by a form of optimism: "But perhaps the very rarity of a serious left forum in these times makes a journal like NLR more valued." I think that's true, but a forum is, precisely, a space in which to meet and talk, an agreed place in which to disagree. The metaphor signifies a distance from political action, as well as the distance the journal has travelled from the hopes of the 60s. "Can a left intellectual project hope to thrive in the absence of a political movement?", she asks. "That remains to be seen." Even "thriving" may be a lot to ask for. "Fail better" may be as high as the mark should be set for now, with an unblinking awareness of the piquancy that attends the conjunction of political allegiance and Beckettian motto.

Perhaps a sense of having been chastened by world history is becoming to a journal in middle age. Just occasionally, I still feel queasy when confronted by the familiar abstractions, confidently used in the singular. When I'm told, for example, that "the thought-world of the west" is increasingly determined by "Atlantic-centred structures of wealth and power", dragging academic disciplines in tow, I find myself feeling that the search for pattern and causation is starting to lose sight of something no less important – the uneven, awkward diversity that is apparent when viewed from a little closer. All intellectual inquiry is a see-sawing between abstraction and particularity, and NLR's inheritance can still make it seem more indulgent of the former than the latter. Interestingly, the language of "determinants" and "system" falls away when it comes to self-description. "NLR stands outside this world," Watkins writes, "defines its own agenda." Excellent, but might not some other elements in "the thought-world of the west" be doing the same, in their own way? Still, the audacity is admirable: I like the thought that a specially unillusioned, independent, global perspective on what's happening is to be had from a side street in Soho.

When so much of even the so-called "serious" media is given over to celebrity-fuelled ephemera and the recycling of press releases and in-house gossip; and when the academic world is struggling to mitigate the worst effects of funding-driven overproduction and careerist modishness; and when national and international politics seem to consist of bowing to the imperatives of "the market" while avoiding public relations gaffes; then we need more than ever a "forum" like NLR. It is up to date without being merely journalistic; it is scholarly but unscarred by citation-compulsion; and it is analytical about the long-term forces at work in politics rather than obsessed by the spume of the latest wavelet of manoeuvring and posturing. Despite its self-description in its guidelines for contributors, the journal is not in any obvious sense "lively". It is downright difficult (but none the worse for that), because what it tries to analyse is complex and its preferred intellectual tools are often conceptually sophisticated. It is difficult where being easy would be no virtue, difficult where aiming to be "accessible" would mean patronising its readers, difficult where ideas need to be chewed rather than simply swallowed. That's what I admire above all about NLR: its intellectual seriousness – its magnificently strenuous attempt to understand, to analyse, to theorise.

So, no balloons, and definitely no party lines. No cheap consolation, ­either. But hey, respect: no question.

• This article was amended on 24 February 2010 to delete a sentence saying that NLR's finances were unclear with rumours suggesting that Anderson family money subsidised it. It has been replaced with a sentence saying the publication has long been self-financing.