The action-RPG digging-platformer spawned from the Minecraft phenomenon, Terraria is bursting with proceedurally-generated co-op content, great pixel-art, and a cool difficulty curve. I've sunk more hours into more new and long-played games of Terraria than I do with almost any game -- and I play a lot of games, people (see my Steam library). At a throw-away $2.50 to $10 (depending how patient for the euphoria-inducing Steam sales you are), Terraria is a sweet bargain for hundreds of hours of good, good gameplay. I recommend for most humans.

For years after release, the creators just kept churning out free content. In sheer hours, this game has a ridiculous amount to consume. I don't have as much fun as many blocking up a big piece of artwork, but the gear-focused character and world progression, strong exploration drive, and solid gameplay make this title a joy to play, and to recommend to all your friends.