Freakin' Terraria, man. Bought it for just six quid on release day and it's gotten me almost 3,000 hours of enjoyment. And I'm one to flit from game to game, too - my library's huge, but Terraria is just that one game I keep coming back to. Just one more playthrough. Let's see what I can get up to this time... (Especially with the new Remix seed!)