So, any of you who liked Half-Life or any of those old-style shooters, you'l love this game... It's been hailed by many as the best game ever made and I'm sure you've heard about it, but if you've never played it, you should. The only way I can really describe it is Fallout 3 + Half-Life... (amazing, right?) It's a very old game, this being the case the graphics are absolutely terrible and I can't help but laugh at some of the voice acting, but the gameplay is just so damn good that it makes up for all of it's flaws.
It's going for $10 on Steam, and it's certainly worth it, but I'm sure you could find it somewhere else for cheaper if you really wanted (I'm not going to look, Steam is just too damn convenient.)
Deus Ex (on Steam) - http://store.steampowered.com/app/6910/