The wait for Terraria: Otherworld is ongoing, but in the meantime it's well worth catching up with the first game, which is 40% off today on Steam's daily deal.
If you don't mind doing a lot of mining, Terraria is a expansive, absorbing open world sandbox game, and one of the best games to come out of the Minecraft craze. While '2D Minecraft' is an easy way to capture the game's essentials, under the surface it's actually a really cool sandbox RPG with exciting weapons and armour, and huge apocalyptic bosses.
It's also great in multiplayer, and there's a busy modding scene. It's a lot of game for £4.19 / $5.99.