Both those games are on steam sale, I'd just recommend buying the base game for each of them. I've completed Dark Siders 1 on Apocalyptic mode and it's pretty fun. It feels like a combination of Ocarina of Time and God of War. It steals from a lot of games or (pays tribute) however you look at it, but it's really fun. I've heard good things about Dark Siders 2 (not Dark Souls 2), where it's more like an Elder Scrolls game with a bigger world, a talent tree, and loot with stats on it (dodge, str, stam, etc..). Fun game highly recommend it at that price.


Also if you have friends to play with L4D 2 is on sale (as it often is) for 5 USD. Definitely fun with friends.