Calling something a "black comedy" doesn't make it good. It makes it a black comedy. There is a such thing as bad black comedies, and Observe and Report is one of them. It suffers from a poor script and a blase direction style. That's why its reviews have been from bad to mixed, universally.
Normally I'm quite the fan of Seth Rogen going back to the classic shoulda-been, Freaks & Geeks. Having said that, I knew that Observe & Report was not going to be like his other films (which is fine). The problem is that Observe & Report doesn't know how to be a successful black comedy. It tries to ride that fine line between drama and comedy (that's the trick), with a big-name comedic star. This has been done previously with a personal favourite of mine, Punch-Drunk Love (also a black comedy). Observe and Report lacks that films' emotion and innovation, and doesn't really go anywhere.
The story is far from original, or engagin: Ronnie (Rogen) is a bipolar mall cop who dreams of being a real cop. Ray Liotta is a real cop who resents Ronnie. That's a pretty far from original setup. Ronnie tries to prove himself, repeatedly, and fails. Eventually he redeems himself, but not before the audience is treated to some unnessesary full frontal male nudity ad nauseum courtesy of the film's resident flasher. Which of course is a cheap comedy trick, not a black comedy trick.
Part of the problem with this movie is that Rogen's character just lacks charisma. You're never really rooting for him during the entire course of the movie. You see his mistakes coming for miles, like a freight train in the night. Yet he steers right into those mistakes, and when they happen you just feel like saying, "Well, I saw that coming..." You never really totally feel for the guy, and that's not Rogen's fault, it's really just the script.
Example: As I said, he's bi-polar. At one point he falls for Anna Faris' character, and he thinks it went well, and he's happy. So of course he thinks he's cured and he takes himself off his medication. I'm sure you can predict what happens after that.
The soundtrack to this movie is one redeeming quality. It really is excellent. Anna Faris is another redeeming value. She's a very underrated actress, and here she plays that vaccuous mall/party twenty-something girl of today just bang-on accurate.
Not a great film. A one-watcher. Rent or buy cheap.
Oh! And "halarious" is not a word.