(MA15+) ***

Director: Aubrey Powell.

Cast: Eric Idle, John Cleese, Michael Palin, Terry Gilliam, Terry Jones, Graham Chapman.

A JOKE is never as funny the second time you hear it, yet somehow the humour of Monty Python still gets laughs, despite being roughly four decades old and everyone knowing every line, every nuance, and every punchline (or lack thereof).

It's testament to the ground-breaking talent back in the day of these Beatles Of Comedy that people still want to see those same sketches, and that fans have been clamouring for a reunion - any reunion - of the five surviving Pythons.

So it here it is - 10 shows live in London's O2 Arena, the first of which sold out in 43 seconds and the last of which has been filmed and beamed into cinemas around the world.

It's three hours of nostalgia-inducing hilarity, or, to be more accurate, it's more like one and a half hours of nostalgia-inducing hilarity by the time you take out the ostentatious dance sequences, the 15-minute intermission, the instrumental musical interludes, and the awkward final ovation.

Being there would have been a very different experience and the complex dance/musical numbers might have seemed more fitting and exciting, but on the big screen - when all you really want is the absurd humour - they just seem to break the flow of the production. Where are the innovative linking jokes that made Monty Python's Flying Circus such a revolutionary sketch show?

Obviously the dance numbers are stalling for time while sets are prepared and the five Pythons can get into the appropriate costumes, but some of them really drag on (particularly The Penis Song). Mind you, they do prevent the show from relying too much on old clips (although seeing a bit more of the late great Graham Chapman wouldn't have gone astray), which would have also felt like a bit of rip-off.

These big production numbers are obviously the work of Eric Idle, who was responsible for the live show's staging and who has spent the past decade turning The Holy Grail and Life Of Brian into a Broadway musical and oratorio respectively. Some of them work wonderfully - a ballet version of Sit On My Face is suitably "Pythonesque" - but some don't - an extended number that merges the Nudge Nudge sketch into an intro for Blackmail feels tacky.

It's the sketches we want, and that's when this is at its best. The Spanish Inquisition, Dead Parrot, Exploding Penguin On The TV Set, Four Yorkshiremen, Crossdressing Judges, Argument Clinic - if these words mean anything to you then you'll be in stitches.

Cleese and Palin are still as great as ever and put everything into their performances while Gilliam seems over the moon about being on stage and his enthusiasm is infectious.

Sadly Jones seems a little lost and befuddled by it all, while Idle seems more interested in getting the 15,000-strong audience to singalong when he's playing guitar.

The sketches are predominantly great. Some new material wouldn't have gone astray (a video post-script to The Galaxy Song is a rare and hilarious addition), which makes the bits when they go off-script or mess up welcome and endearing. Cleese and Palin taking their time to get through the Dead Parrot and Cheese Shop sketches is a definite highlight.

Like most reunions, Monty Python Live (mostly) is good at reminding you how great these guys were, with 'were' being the key word. It's unmissable in one sense because it's the only reunion we're going to get, and the warm fuzzy feeling of seeing the Python team restaging these classic sketches or singing Always Look On The Bright Side Of Life makes it well worth seeing.

Keep your expectations low, and you'll be transported back to their glory days. Then go home and watch the TV show and listen to the albums, and all will be right with the world.