Terraria
Terraria is a complex project that offers you innumerable adventures in the world full of mysteries. You are not limited with quests or plot.
Right from the start you are able to go wherever you want and write your own story. Explore the wide terrains and find new items and weapons.
While you are travelling, you may enter different locations where you will obviously meet various creatures. Some of them are friendly and the others are not really. In such a case, use your weapon and pick a fight. You may get unique prizes for defeating some bosses.
When you find the place that will look the most pleasant to you, build a home there! Use the resources you found all over the world and construct a wonderful house. And if you get bored, invite some people to live there, too. They will gladly move to the place and probably share some materials with you.