It could be argued that Minecraft was a 2010 release, but it just came out of beta in November, so we're putting it on the list; anyway, it's so great, it should be on the list every year. Minecraft isn't a complex pitch: you're in a very big, rather retro-looking low-res world. You can walk around, you can pick up things, and you can make other things out of them. While you're doing this, various animals try to eat you. The end. The complexity comes from you: the Minecraft universe is so endlessly, pleasurably reconfigurable and customizable that it rewards you for the zillions of hours you sink into it by becoming a reflection of your imagination.