It's Edgar Wright's weakest film to date. Scott Pilgrim vs. the World is a hard act to follow up, though.
It was fun to see Simon Pegg and Nick Frost in 'reversed' roles, but there were times when Simon Pegg was hamming it up a little too much--at least in the first 20 minutes.
Without giving anything away, at the end my wife and I both agreed that we thought it was kind of trying to be like Cabin in the Woods--where it keeps on turning into a different kind of movie. It didn't work nearly as well as Cabin in the Woods, but I can still see this winning a cult following on it's own.
Like Frank said it gets surprisingly dark. They hide it in a way by glossing over some of the darker details of the story--kind of like how Shaun of the Dead has a sort of dark ending that plays out like a funny, happy ending. It's amped up here though.
Still, it's pretty damn funny. It's best if you go into it without knowing anything, like This is the End or, as I mentioned above, Cabin in the Woods.
It probably also gets funnier on repeated viewings, but as I left the theater last night I didn't feel like I needed to see it again. Solid three star movie.