Sounds like a guy who likes shooters.
I recommend Just Cause 2 (which is currently on sale for $3 at 80% off). It's an open world shooter/action game. Has a massive map, tons of weapons and vehicles, tons of things to blow up and destroy, and the protagonist is equipped with a grappling hook (the best grappling hook in any game) and parachute at all times, which can create some interesting gameplay scenarios.
The game has been out for many years now so you can pop over to youtube and take a look at some gameplay videos. It's a pretty ridiculous game.
Also, the Bioshock games would probably be right up his alley. Bioshock 1 and 2 are currently $20 each on steam and Bioshock Infinite is $40, but those prices will go down to $5 and $10 during the winter sale.
Natural Selection 2 might also interest him. It's a class based multiplayer FPS where one side plays as Space Marines and the other side plays as aliens. The twist is that each side also has a commander, one person who plays the game like an RTS, issues orders to their group, chooses what upgrades to build and how to expand, and gives health to injured players. It's kind of a difficult game to get into but a lot of fun once you understand the mechanics. It's $25 right now but will go down to about $7 during the steam sale.