4.The Elder Scrolls V: Skyrim
Skyrim is less a game to be played as it is an entire encyclopedia set in front of you.
Endless options of play will take you in countless directions. Follow the main quest or become a leek farmer in your enormous house in the hills. With the sheer amount of freedom and detail you could play for years while never engaging in the main storyline.
Wandering and discovery are the most exciting part about this game.