As scarred already said, if you want to play games on MBA maybe it's better to wait for an updated version as it probably will have some other improvements other than the HD4000 (better cooling perhaps?).
However, I play WoW on my MBA 2011 for over a month now, daily for over 2 hours sometimes and while it does get a little hot, the game runs smooth on lower settings. If you don't mind lower quality settings like me - you will be pleased.
It's always good to have a cooling pad, though. I have purchased an aluminum one that is very quiet and keeps my MBA cool even when playing WoW.