Knocked Up is funny. Laugh out loud in the theater funny. This movie is certainly not for everyone, especially people who don't like: 1 - Nudity 2- Dumb guy jokes (farts and stuff) 3 - Sex jokes 4- Bad language 5 - Gross stuff
I do like Seth Rogen as Ben who reminds me of a combination of Will Ferrell and Jack Black. Katherine Heigl's character is nothing like Izzy from Grey's Anatomy so don't worry.
Overall, I recommend this one, although it does take a turn for the worse towards the middle-ish end and starts acting like a romantic comedy.