I was going to write sort of a long review, but I don't really feel the need. It's smartly written and well-acted pretty much through and through. There are a couple parts that aren't as tight as they could be but it's still a pretty impressive work. The main points I'd hit are:
1) It makes a complex and very dry plot (programming, corporate finance, intellectual property, etc) not only clear but relevant and interesting without trying to make it into more than it is. There's a little bit of pontificating and a line or two here or there that's sort of... trite or muddled or whatever else (although, at times that might be intentional, I could definitely make that argument) but it's generally very sharp.
2) Mark as a character is really fascinating because he's not likable, or even especially sympathetic, yet there's something about him that makes you
want to sympathize with him and Jesse Eisenberg does amazingly well capturing that--the whole of the character is in slight variations in his intense speaking pattern or subtle changes his generally expressionless face. You don't notice how well done it is until you go back and think about it.
Also, I'm glad a movie finally used Justin Timberlake right.