The beginning was a little slow, though there were quite a few laughs. The big thing with this movie is the high number of cameo appearances, including the much-talked-about Tom Cruise. Sometimes they're more than small appearances, sometimes they're only brief. But all of them are funny.
The acting in the movie was done really well, I thought, all around. Ben Stiller and Robert Downey Jr., though, were the obvious leads of the film. The majority of the movie concentrated on those two actors' characters. Jack Black's character isn't really the typical Jack Black, in my opinion (musically obsessed, hardcore spaz). But then again, Black wasn't at the forefront of the movie, either. Brandon Jackson is pretty much like you'd figure him to be from the movie trailer. But the surprise of the group was Jay Baruchel, who really held his own against these other guys. You'd probably only recognize the guy from Knocked Up (the scrawny friend with the bad haircut). But his character here, though he's not one of the top billings, played a bigger role than arguably even Jack Black's. And his character was much better, too. Of course the stand-out was Robert Downey Jr. Anytime he was off-screen, I waited for it to go back to him (even though you could barely ever tell it was him). Oh, and Tom Cruise's character is hilarious. He was very good, too. As for Nick Nolte? Well, he was Nick Nolte (intense and kinda creepy).
The cinematography was another thing done quite well. There were a lot of great scenery shots, as well as fun action shots. And on the subject of action, there was a lot, and it was all excellent. The only bad visual I really noticed in the whole movie was toward the end, when there's this kid stabbing one of the characters... and the whole sequence with the kid (from the stabbing to what happened right after) looked really fake. Otherwise, it was great.
So we have the action down; what about the comedy? For an action-comedy, it's half the equation. And it really worked. I was laughing, my theater was laughing, and it was hilarious in its absurdity. And the humor ranged all around the board: from just verbal humor, situational humor, gross-out humor, action-related humor... well, the movie was just really funny. I can't say much more than that.
And I really don't think I can say much more than that. The acting was done well. The visuals (in both cinematography and action) were done great. The humor was great. The cameos were great. All around, the movie was highly entertaining (except for a few slow spots toward the beginning), and I left the theater smiling. What more can you ask than that?