Maplestory - MapleStory is among the most popular of MMO in the 2D area scrolling style offering a user count will into the lot of players.
Underworlds - Underworlds is one of the few video games on the app store to capture the older action RPG feel.
Path of Exile - Path of Exile is a free to play online action roleplaying game that draws clear inspiration from Diablo but charts a path all its own.
Hammerwatch - Hammerwatch is a fast moving and easy adventure set in a fantasy game world.
LaTale - LaTale draws heavily from some other 2D side scrolling video games to provide a great fantasy MMORPG world.
The Binding of Isaac - The Binding of Isaac is a 2011 independent video game designed by Edmund McMillen and Florian Himsl.