Which generation were you referring to? I have the late 2011 Macbook Pro, and it ran games like Diablo 3 well enough for good game play, but basically ran the more graphic intensive games like Tomb Raider laggier which prompted me to lower the settings, after which they worked serviceably fine. I'm sure the newer editions would run better on the same games.
I have the early 2013 13" with the HD 4000. For my needs it runs just fine. I only ever play DOTA 2, TF2 and a few older MMOs. So far no problems. The only game I have to slightly lower graphics are on DOTA 2.
I have an '13 with the i7 and gaming on it isn't horrible. I don't play long to keep from burning up the video RAM. It does sound like a jet engine after 5 minutes of playing any game.
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