"Limitations are the soil from which creativity grows," somebody once said – but obviously not when Frankie Boyle was within earshot. Frustrated by the BBC's anxiety surrounding offensive comedy – his remarks about swimmer Rebecca Adlington and the Queen's haunted "pussy" caused particular ire – Boyle quit the corporation's panel show Mock the Week. Now he has resurfaced at Channel 4, in a format that's being sold as Boyle, uncut at last. But after its first episode, one finds oneself wishing Boyle back into the BBC straitjacket at the first opportunity.

Tramadol Nights – the title refers to a synthetic painkiller similar to morphine – splices excerpts from Boyle's standup with new sketches, in which the Glasgow comic demonstrates an unexpected penchant for acting and American accents. The standup sequences will be familiar to those who've seen Boyle on his recent, 113-date tour. And the sketches suffer from the same problem that made that touring show Boyle's least exciting. When he first appeared on the comedy scene, Boyle was a brilliant joke-teller, many but not all of whose gags were tasteless. Now – onstage and in Tramadol Nights – he plays up to his own publicity, as a comic known for heartless sensitivity-baiting and not much else.

And so the first episode brought us sketches that recast 1980s TV show Knight Rider as the imaginings of a deranged, vomiting junkie, and 1990s movie Green Mile as a tale of a condemned black prisoner who can cure the sick by "fucking" them. (Whether these retro skits honour Channel 4's promise of "no-holds-barred standup [picking] apart all aspects of modern life" is a moot point.) Elsewhere, there was a cartoon sequence called George Michael's Highway Code, a queer-bashing scene about Brokeback Mountain – the whole episode was obsessed with (usually gay) sex – and a title sequence to Loose Women Iran, at the end of which the burqa-clad presenters were hanged.

It's difficult to resist the conclusion that, with Tramadol Nights, Boyle has just been given enough rope to hang himself. But, alongside the squalor and animated spunk, there are flashes of the caustic wit that make him great. The BBC gets it in the neck with a sketch called Untitled Street, a series so cautious of offence that the actors' faces are blanked out and the dialogue takes pains to say nothing whatsoever. And, even to those of us who've heard the jokes before, there are laugh-out-loud moments in the gleeful, vicious standup sections of the show. Painting his imagination in lurid word-pictures is what Boyle does well. Acting it out in three dimensions, so far, isn't doing him any favours.