Although this (the director's cut) was perhaps just a little long, I really enjoyed this film and laughed till I cried in more than one place. But it is a film where you sense that not everyone will like it. Some of the comedy is direct and irresistible: the verbally absurd, like Downey's gibberish Chinese when trying to con the leader of the drug-band or the visual humour of Stiller running along with his "son" stabbing him in the back until Stiller finally throws him off the bridge. But some is conceptual humour: remembering the idea of just what you are watching right now, or registering that the occasionally stupid, trite dialogue is crafted that way parodically.
If you are considering getting this film, my advice is stop reading any other review when they mention Tom Cruise. I have noticed that some reviewers describe the nature of his role: for me this is a spoiler! When you finally realise who he was during the credits, this is one of the funniest surprises in the film.
The film is also justly well known for the trailers at the start, these are very good, but they are by no means better or even as good as the best moments in the film proper. Its main faults are overlength - a few cuts would have worked wonders (a pity that you can't choose between Director's Cut and Theatre Version, as with so many BDs these days) - and that the opening sequence of the film until they stop rolling is not THAT funny.
As parodies go this is not in the league of "Austin Powers", which was much better as dissecting the cliches and idiocies of older Bond movies than this is at sending up war movies. But this film gains extra dimensions through ridiculing the self-importance and pretensions of Hollywood, and this provides much of the best humour. Being vague to try and avoid a spoiler, I'll say one of the funniest bits is when the studio boss does not change his attitude at all after realising his rather large initial misunderstanding.
Highly recommended, and the picture and audio quality are very much worthy of Blu-Ray. Enjoy