Dara Ó Briain, Hammersmith Apollo

At 6ft 4in, Dara Ó Briain is a massive bloke. With his bald, cannon-ball head and barrel-chested torso – togged out in a suit – he looks like a bulldog that's acquired a tailor. But it is not, of course, his physical build that has made this affable Irishman a huge name in the entertainment industry. What's key to his popular appeal is his "ordinary bloke" manner combined with his gift of the gab and his quick mind.

As an observational stand-up, he surely won't be running any marathons around the stage. His list of satirical butts, after all, includes fitness trainers' quackery. Why on earth would anyone, he asks, waste time exercising muscles they haven't used in years, as if that's a plus? The muscles are clearly redundant, so let them rot!

It is Ó Briain's mouth that's motoring. The rate of words per minute is remarkable, effortlessly so it seems. He's an absolute pro, barely fluffing a phrase in two-and-a-half hours of energetic chat. His air of lively engagement never flags, as he leans eagerly towards the audience from the stage.

His material isn't electrifyingly original. Indeed, you can see formulas shaping the show. The first half is based around that old chestnut of asking those in the front-row seats where they're from and what they do. None the less, his ability to bounce off the audience's contributions, with off-the-cuff wit, is heartily enjoyable. Having ascertained that one punter is a security man called Chris – who works nights for Next – he is soon envisaging a scenario of fey patrolling in the latest frocks, with a little riff about Chriscross-dressing.

Moving on to ask what dreams anybody has had involving celebrities, he bizarrely gets a woman volunteering that she had had one – about a squirrel. She gave birth to it in the dream. Almost dumbfounded but then loving the insanity of this, Ó Briain delightedly proclaims it to be "the weirdest opening to a gig that I've ever done".

Overall, he seamlessly interweaves such impromptu exchanges with pre-prepared material that has stood the test of time. He also likes, habitually, to mention subjects that he's not going to bang on about, only to use that as an opportunity to drop in two or three gags on those very topics. So, he's going to steer clear of religion, is he, on the very day when the Pope is in London? Of course he isn't. He's the host of BBC2's Mock the Week, for heaven's sake, and a well-known atheist from a Catholic background.

The ensuing gags are hardly excoriating. Jonathan Swift, he ain't. However, there's a nice anti-Islamophobic twist when he rebuffs the Christian Right's apparent complaint that he has been pusillanimous in scoffing at Rome but never at Muslims. No Muslim, he ripostes, ever forced him out of bed on a Sunday morning to listen to 40 minutes of baloney, or made him give up sweets.

If a theme emerges when Ó Briain gets into his more substantial set pieces, it's the cobblers that we're sold and the stupidity rife in today's culture. In a clutch of anecdotes about the ludicrously PC editing his newspaper articles have suffered (among other things, Ó Briain does a weekly sports column in The Guardian), he recounts how one quip about the Irish potato famine was nervously excised. How sensible, he says sardonically. A lot of those cases are still going through the courts, are they not.

With his wife being a surgeon, and as a science graduate himself, he particularly relishes sending up the hokum disseminated in ante-natal classes. He enjoys getting slightly outré at this point too, throwing cheekily graphic bits into the mix.

Then he's off, laying into blockbuster movies, especially 2012 where risible cod-physicists cry "The neutrinos have mutated!", followed by hours of John Cusack inexplicably running away from lava. What follows is a lengthy and surreal dissemination involving Ó Briain running madly aroud the stage. For a burly bloke, he's hilariously good at physical comedy.

• Dara Ó Briain is at Hammersmith Apollo, London W6 until 25 September, then touring until 25 November
• Find Dara Ó Briain on Amazon