Given my love of The 40-Year Old Virgin, one of the defining films (let alone comedies) of the decade, a letdown was inevitable. But I was still expecting a lot more than I got from Knocked Up, which tries and fails to resonate like its predecessor.
The heart of my objection is in Knocked Up's refusal to play by its own rules. The film is littered with astute observations about parenthood, marriage, and adulthood. But the sheer quantity of laughably contrived behavior on the part of each main character invalidates all of those observations. The setting is Sturges, but the story is Shadyac, i.e. a bunch of horseshit. It's a sheep in wolf's clothing... a fairy tale hot dog slathered with the mustard of modern-day moral philosophy. (Sorry.)
A model relationship... circa 1832
Don't get me wrong. Knocked Up is hilarious. Just as a comedy, it succeeds. But once it starts taking itself and its story seriously, the whole thing falls apart. It tries to be more than just a funny movie, and fails. While I respect the effort, its failures reflect on the rest of the movie.
Instead of another 40YOV, it's another Wedding Crashers... a very funny movie with lots of caveats.