It's now 30 years since the publication of the first Hitchhiker's Guide to the Galaxy novel. Yet though the subsequent period of Hitchhiker-mania – by 1984 encompassing two radio series, four novels, a TV series, computer game and three major stage productions – may be over, the phenomenon has proved as indestructible as its constantly reincarnated bit-part character, Agrajag. A fifth novel was published in 1992 and the franchise even survived the 2001 death of creator Douglas Adams: a film version and three further radio series have appeared within the last five years.

This month, the story has once again hit the headlines thanks to the imminent publication of a sixth Hitchhiker's novel, And Another Thing by Eoin Colfer, the bestselling Irish author most famous for his Artemis Fowl series. Judging by the frenetic blogosphere coverage it has generated, many are still obsessed by this tale of intergalactic high jinks. Others, however, remain immune to the charms of a story most famous for its manically depressed robot and comedic use of the number 42. After all, isn't it just for science fiction geeks?

I don't think it's only concerns over self-image which would cause many fans to answer with a resounding no. For one thing, it's debatable to what extent Hitchhiker's is science fiction at all, but however it's tagged, the cosmic setting is, to me at least, all but incidental. Adams himself insisted he hadn't set out to write science fiction, but simply found himself without many other options after he blew up the Earth in episode one of the original radio series. And although he expressed admiration for Kurt Vonnegut and Robert Sheckley, Adams's main literary influences, AA Milne and PG Wodehouse, were notably more earthly.

True, he did spend a period writing for Doctor Who, but he also wrote for Monty Python's Flying Circus; in many ways, Hitchhiker's has far more in common with the latter series. Although the majority of the saga is set on distant planets, and contains plenty of real-life science and technology, at its core it retains a thoroughly surreal and very English sense of humour. Such a combination might sound incongruous, but it's a formula which would help pave the way for everything from Red Dwarf to Men in Black (the latter, admittedly, rather more transatlantic in its comedy).

The story's most fundamental themes, meanwhile, include such reassuringly earthy – and earthly – subjects as cricket and towels. Yes, this is a story populated by such exotic characters as Gargravarr, the disembodied mind in charge of the Total Perspective Vortex, and Eccentrica Gallumbits, the triple-breasted whore of Eroticon Six. Yet there are also mentions of rich tea biscuits, Islington shops, Which magazine and American Express cards. Spaceships await deliveries of lemon-soaked paper napkins; aliens watch gameshows and take holidays in Bournemouth.

Main protagonist Arthur Dent is more Peepshow's Mark Corrigan than Captain Kirk, sporting a dressing gown, forever in search of a nice cup of tea, and responding to his enforced interplanetary adventures with disgruntled, beta-male sarcasm. Ford Prefect, his alien companion, likewise favours drunken parties over Star Wars-style heroics. As Stephen Fry, one of the series' most noted fans, told the South Bank Show, he was first attracted to Hitchhiker's because, in contrast to most science fiction, "it was absolutely on a human scale".

The broad appeal of Hitchhiker's can be measured, in part, by the sheer range of high-profile figures involved in its various incarnations. The five radio series, for instance, have found room for New York comedy legend Jackie Mason, astronomer Patrick Moore and Hollywood star Christian Slater, a group whose eclecticism is only enhanced by the additional presence of Richard Griffiths, David Jason, Rula Lenska, Joanna Lumley and theatre maverick Ken Campbell. Alongside Martin Freeman, the film version featured Alan Rickman, John Malkovich, Helen Mirren, Bill Nighy, Bill Bailey and the rapper Mos Def. Either list is a far cry from any standard roll call of SF fans.

But The Hitchhiker's Guide to the Galaxy is not without its faults. Plots, for instance, can be weak, in part due to Adams's notorious inability to hit deadlines. Large portions of the saga were conceived at the last possible minute, often under house arrest by whoever had the misfortune to be his editor at any given point. The third novel, Life, the Universe and Everything, sees Adams mercilessly cannibalising pre-written stories, with decidedly mixed results, whilst its successor, So Long, and Thanks for All the Fish, is a soppy affair apparently betraying troubles in its author's own love life. (Thankfully, the bleak Mostly Harmless represented a significant return to form.)

Also – and sadly this is a trait which does chime with science fiction stereotype – the Hitchhiker's universe also suffers from a lack of women. Trillian and Fenchurch, the only significant female characters, are almost as two-dimensional as Random, Arthur's rather clichéd adolescent daughter, who shows up in the final novel.

For all that, however, the Hitchhiker's saga remains thoroughly deserving of investigation – both on its own terms and for its wider contribution to contemporary popular culture. (Purists, incidentally, would advise starting with the first radio series.) It should perhaps be glossed over that revoltingly slick funk-pop act Level 42 are reportedly named after the story's most famous gag, but take heart from the fact that Sanjeev Baskhar's The Kumars At No 42 was so named for the same reason. The Babel Fish online translation service is just one other example of the story's reach, as is the popularity of its various catchphrases – including the one which should be borne in mind by all Hitchhiker's newbies: "Don't panic".