'Disco Stu said:
Thanks. I'll look into the Halo series and the Earth Defense one for sure. And yes, downloading from the Arcade is a good option too. I'm pretty sure the first thing he'll ask is if he can download Minecraft.
Everybody has made some good suggestions. Minecraft is a perfect game for a 10 year old. A complete sandbox to do anything in without really any killing or violence.
Lega Star Wars, Batman, Harry Potter etc is also perfect. No blood. Plays through the movies he may already know if he's seen them. Some minor critical thinking and puzzle solving. Good clean fun.
Halo is about the edge of T or M you want to get to at that age. There's violence but it's against aliens. Still fairly realistic. Probably your discretion on whether your kid can handle it.
Call of Duty, even the old ones (2 and 3) are pretty graphic. You are shooting and killing human beings. Even if they are nazis, they are still humans. Up to you on that one.
You got portal 2. I'd definitely recommend portal 1. Will provide some backstory as well as give a better basis for the controls. Lots of good sarcastic humor that will probably go right over his head.
Any sports game of his liking is available to you for pretty cheap. Just get older year versions of any sport for probably $10.
Lots of stuff to choose from really. Enjoy the bonding with your kid.