I think this review said it perfectly:
An Amusing Bit of Fluff
The premise of this movie is terrific: Celebrities play themselves in a comedy about the end of the world. It's fun to see celebrities mock themselves, particularly a coked up Michael Cera, and much of the charm of the first scenes is simply seeing actors play with the concept.
I enjoyed the movie, but I can't say I loved it. It's funny, but it's not hilarious, and while the bits build and there is a sort of story, it's not fully developed because it's essentially a vehicle for the humor.
Also, the frat boy humor just wears thin. This movie is inordinately fond of jokes involving bodily excretions and genitalia, and what can be outrageous and edge in the first ten minutes can feel like a dead horse as the second hour commences.
It's nothing anyone really needs to watch, but it's a fairly enjoyable way to kill a couple of hours.
I gave it a 7/10. I was amused, it had it's few moments, thus if the Rapture ever does come I'll probably miss it for enjoying this film even a little, but there it is. I was surprised it only had a budget of $32 Mil, seeing the amount of stars in the cast and the special effects involved. It looks to have grossed over $126M worldwide.
It's worth watching the once, but I wouldn't advise anyone to go expecting a major blockbuster here.