I went to see it Saturday with very low expectations, and it failed to meet even those. I knew it was gonna be bad, but I didn't think it was gonna be that bad. The movie's biggest problems are Rogen and the script, neither of which work for this kind of movie. It's like Rogen and his writing buddies decided to brainstorm the script while they were stoned and used every bad idea that came to mind. Rogen's Britt Reid is a dim-witted/spoiled rich kid/party guy who apparently still hasn't outgrown his early college days, and Rogen's performance isn't too dissimilar from his appearances in The 40-Year-Old Virgin, Knocked Up, and Pineapple Express. "Stoned" would also explain the "comedy", 95% of which simply isn't funny. Tom Wilkinson, Christoph Waltz, Edward James Olmos, and even Cameron Diaz (who I don't think much of, to be honest) turn in good performances considering how little they have to do in the film, but these thankless roles could have been played by almost any other actors and it wouldn't have made any difference.
IMO there are only two good things about the movie--Jay Chou as Kato, and the Black Beauty. Like the more experienced actors I mentioned above, Chou's performance is better than this horrid movie deserves; reminiscent of Bruce Lee in the '66 television series without being a direct imitation. And the Black Beauty looks better in this movie than it ever did in the television series--slightly updated, it looks lower and sleeker, and it's simply a gorgeous car.
My recommendation: Wait for The Green Hornet to come to cable, then watch something else.