Why it's similar: The tagline for the game says it all: "survive, discover, explore, and fight." That's essentially what Starbound is all about. An infinite universe means there are loads of possibilities in this cooperative 2D game when it comes to shaping the world, and also finding new locations to set up shop.
What makes it unique: Like all good stories, Starbound is all about the journey and not necessarily the end goal. Exploring the game with friends--whether it is just to farm, try your hand at space exploration, or create weaponry for quests--is fresh every time. While it's open-ended, quests and NPCs make the game feel like it has more of a purpose, with a story to boot.