I play WoW on my aluminium MBP and it runs fine. I have most settings on high, and I have never had any frame rate issues. In Dalaran I average around 20-25fps, whch is pretty good considering.
One thing to note with this model is that the ventilation is kinda poor, when I start running intensive programs/games the fans ramp up and the thing sounds like it's about to take off. However, there is a nice freeware app out there where you can adjust the threshold values of the fans which helps. This doesn't bother me though because I use headphones which block it out nicely.