The new 2D side-scroller is called Sonic Runners. It is a new free-to-play offering. While it is free-to-play, you can apparently purchase premium items with in app purchases.
Using an innovative control scheme where you can play the game with one hard, Sonic moves forward and you tap to jump. The included stages are designed to be played in a minute or two, which is again unique to the Sonic franchise.
Sonic Runners is slated to arrive later this spring and it is apparently going to skip the consoles this time around. However we hear an Ouya release is at least possible. Lets at least hope that Sonic Runners has a better fate than Sonic Boom which bombed very big on the Wii U.