Yesterday, Terraria launched it's new version, Terraria 1.2. It's a major update which features lots of things, such as new ores, weapons, armors, over a thousand new enemies, including the new bosses, and some friendly NPCs.
For those who do not know what Terraria is, is a side-scrolling, platform, sandbox. Some call it Minecraft 2D. I'd prefer to say that Minecraft is Terraria in 3D with a lot less things.
The game centers around in making your home and stuff so new NPCs arrive. As you progress, things will happen, such as a meteorfall after you defeat certain boss. And after finishing off all the bosses, you can activate hard-mode, which brings all the bosses into it's hard counterpart.
You can check some of the features included in this update here:
http://terraria.wikia.com/wiki/Version_History#Update_11_.281.2.29