21. PlanetSide2 (2012)
A PC MMO shooter that is free to play—but we all know what that means. It might be free to play, but you're going to have to pay to win. Offering in-game transactions for real money is a relatively new, and some would say distasteful, development in gaming. That said, PlanetSide 2 still enjoys a huge amount of player retention for a sci-fi shooter epic. An MMOFPS (massively multi-player online first person shooter) that has maintained a tremendous amount of popularity helped make it on the list.