CoD 4 runs fine on MBA.
I tried it on the 2011 model and 2012 model and both runs fine.
What settings were you playing at, what frames-per-second did you manage to get, and how hot did the machine run?
I dont remember the fps but no lag at all.
Everything is on high.
Pretty hot. Not hot to burn but uncomfortable on your lap.
Civ V will run, but don't try to play with a bunch of other Civs. Game will crawl when you start getting towards the late game and even switching into strategic mode won't help.
Keep it to 4-5 other Civs and it should be good for most of the game.