Fun sandbox game where you play minigames to earn money, and use it to buy stuff for your own condo. If you like GMOD Tower, you'll love it. Low on official content right now, but workshop has plenty.

A charming, fun 4-player co-op brawler. Castle Crashers is just one of those timeless games. Its gameplay has a lot in common with River City Ransom.

DayZ if it were free, less buggy, less confusing, had smaller maps and better servers... but was presented in a blocky cartoon style. Not a bad game.

Postal 2 lets you be a peaceful saint, a psychotic killer, or anything between. It's vile, vulgar, & violent, but hilarious with strong social satire.

Doom. The father of the FPS genre. If you haven't played it, what the ♥♥♥♥ are you doing with your life? Get this, download Zandronum, and play!

After Bethesda moved QL to Steam, Quake Live has improved drastically. Mod support is now in, custom maps, and no more loadouts by default. Worth $10.

Broforce is a fun, and hilarious side-scrolling shooter with tons of ♥♥♥♥ exploding and destructable environments. A ton of 80's/90's action heroes too.

If you like competition, get CS:GO, if you like interesting maps and mods, get CS: Source. Even with GO out there, CS:S is still fun and worth the dosh.

If you played Warframe years ago and didn't like it, try it again. It's a lot better than it was, and the increase in content is phenomenal. Great game.