It didn't really work for me.

Rating: 4/10 (25 July 2009)

Clearly lots of people enjoyed this movie and even found it funny, so I certainly don't intend to insult what appears to be the majority, by suggesting that they don't know what they are talking about. Taste and humour are very personnel, so please read this review as one man's opinion.
The humour on display here, strikes no cultural accord with me, yet is clearly popular in the US, which leads me to assume that this is idiosyncratically American humour (or should that be 'humor'?), though I mean no disrespect in drawing this conclusion. To me it was unsubtle and based almost entirely on put-downs and pratfalls - it was not sympathetic or comfortable; one would definitely have to laugh at someone, there was never that warm inclusive moment when one felt included in a instant of shared humour.
As one would expect from the title the story as a whole was very predictable: This film was always going to rely on the set-up and delivery with the punch line, being less relevant, but not unimportant, since this is where the the audience would expect to find satisfaction: the themes, plot and sub-plots need resolution and vindication at this point and the extent to which this gives closure and satisfaction to the viewer is ultimately what helps to inform our overall impression.
The idea of this movie is fairly well used, but still has plenty of life left in it: we start with a seemingly impossible and certainly implausible scenario and then unwind the story to show how it came about, finally winding it on to the point at which all the issues are resolved. Ideally we should find as the story unfolds relationships and pre-existing problems are also solved and resolved as the characters we come to love, grow as a result of their trials and vicissitudes. Unfortunately I didn't like any of the characters and at best I could only claim to have come to tolerate some of them by the end of the movie. To this extend there seems to be something of a groundswell agreeing with me from my perusal of other comments.
The set-up when it finally happened - it would have been so much better as the opening scene - was reasonably inventive and certainly had scope, but... We had already met the characters by this stage - opinions were formed! I can not believe I am alone in finding the juxtaposition of the Alan Garner character and the baby as anything other than uncomfortable. For me as for every parent, I would assume, the idea of a baby with a character that has told us he is banned from going near schools is completely drained of humour.
From here on the film proceeded as a succession of vignettes and comedy sketches, with the main characters taking a level of damage that would have finished Wile E. Coyote, yet carrying on little scathed. There were uncomfortable moments, but there were no moments of tension. It wasn't that one did not care what happened to these people (though I didn't much), it was more a case that the 'comedy' seemed to imply the characters were indestructible in a cartoon-like way and therefore not requiring of our care or sympathy.
Which leads to the denouement (the punchline) which for me was sloppy and hurried. It was more a mad-cap ticking off of items on a list than a careful and satisfying final weaving of the various story threads into a triumphal and complete ending.
This is definitely for those who enjoy sight-gags and humour that tends to the slapstick end of the comedy spectrum. Those looking for dry humour, one-liners, satire, pastiche or the more cerebral styles will not be so well catered for.
I cannot pronounce against what is clearly not my cup of tea, but by defining what did not work for me I would hope to help others who's tastes might be more conformant with mine own.