You're going to be sadly disappointed with the performance of your 13" when playing games. My 2011 Mac Mini (admittedly HD 3000, not HD 4000 like yours) struggles to play Left 4 Dead 2, a game I don't consider to be very graphically intensive. Chances are, you're going to have a pretty poor experience with BF3. Diablo 3, on the lowest settings, is barely playable on my machine and suffers loads of lag. I know the HD 4000 is meant to improve things, but without a dedicated graphics card, I think you'll be out of luck. All the best, though!