Mirror's Edge is a game I will defend to the end, yet I still am not sure exactly what it does right. I just know it must be brilliant because it makes the palms of my hands sweat like a hog's back (I know, disgusting right?). It certainly was a gem in the rough and had some bad levels, but in general, I really thought it was something special. The first-person basic running gameplay was stellar, the art design was breath-takingly beautiful and a welcome change after the contemporary focus on 'realism' that has been ruining modern gaming art, and the soundtrack worked brilliantly. I agree with the critics in here though that the gunplay was unnecessary - they could have just left it out and it would have been even better. The quicktime events in cutscenes were a completely retarded addition, and the hand to hand timing disarms were pointless.
There's certainly some replayability in there too, with the timed levels.