I thought it was fantastic.
RDJ was amazing, as was Stiller. I agree that Black was a little flat (but when is he not?), but all in all, it's a pretty damn good comedy.
Tom Cruise just rocked his douchebag performance. I even liked McConoughey's character. Everyone pretty much brought their A-game (extra points to Tobey Maguire for his hilarious cameo at the beginning) except Jack Black, but even he wasn't BAD.
Overall, it's not a movie that just makes me laugh out loud, but it's definitely a movie that I'd buy and watch more than once.
Gets a gold star from me.