So I've been playing this game called Starbound lately that I think is absolutely awesome.
http://playstarbound.com/
If you really like building/exploring games like Minecraft or Terraria this game is the same exact concept, except it takes place in space.
The game generates infinite planets with infinite possibilities of life on them. A planet could be a barren waste land with lots of minerals on it or hold a city or base of one of the 6 races in the game. Theres bosses, loads of customization and armor/gear progression. There's multiplayer and PVP and a ton of modding. Oh and guns, lots of shiny guns.
It's only 15 bucks through Steam and I have put 70+ hours into it the last two weeks, and its still in Beta. It is really deep for an open universe crafting/building game and I highly recommend.