Here's a couple of things to consider:
http://www.notebookcheck.net/Mobile-Graphics-Cards-Benchmark-List.844.0.html
Intel HD 4000 - Rank #193 (what's in the current MacBook Air)
Intel HD 3000 - Rank #264 (what's in the previous MacBook Air)
So from that perspective it's an update, 71 spots on a list that's about 450 deep is pretty significant. Just for comparison sake, here's how those cards stack up against the dedicated options in the MacBook Pro
AMD Radeon HD 6750M - Rank #105 (previous generation MBP entry option)
AMD Radeon HD 6770M - Rank #90 (previous generation MBP upgraded option)
That's a huge upgrade and well that's what you can expect when you move from shared to dedicated. The current MBP moves up the list even further.
NVIDIA GeForce GT 650M - Rank #54
For Skyrim they "recommend" a GeForce GTX 260 or ATI Radeon 4890, both of those cards were a top 145 ranking on the same site and even then Bethseda said that's if you want to play the game on "High." I fired up Skyrim on last generations MacBook Air and I averaged about ~ 15 FPS with everything just about turned off. Hardly the way I'd want to play a game like that on a $1300 computer.
For Mass Effect 3 it was playable on the Intel HD 3000, again everything set to low and I averaged about ~20 FPS with it dipping to sub 12 FPS during heavy action sequences. I played it for a half hour and that was about it for me, not fun.
You'll be fine with CS: Source and I've not tried CoD of any flavor.