Well, since a lot of people think Mirror's Edge is bad, I'll say that.
...Wait, what am I saying? Mirror's Edge was a great game! Sure, it wasn't very long, and the cutscenes needed different animation, but the gameplay, graphics, music, and environment were amazing!
I can't help but feel that a lot of people just felt irked that they paid full price for such a short game. Let's face it, if Portal had been sold as a separated game at full price, it wouldn't be quite so universally acclaimed. (Not that I have anything against Portal; it's fucking amazing)
Of course, this is all opinion, but I just can't see why so many people don't like Mirror's Edge.