The latest big Sonic title, with title yet to be announced, will be similar to previous Sonic games, especially Sonic Heroes (in dificulty), since the game’s difficulty will depend on character; Sonic Unleashed (Sonic World Adventure in Japan, daytime stages only) and console versions of Sonic Colours and Sonic Generations in in-game camera, since it will use 2D and 3D (except on the Nintendo 3DS version which will only have 2D side-scrolling, as in the DS Version of Sonic Colours and 3DS version of Sonic Generations) camera view and Sonic Colo(u)rs and Sonic Generations in game graphical differences, as I mentioned before in parenthesis, the use of 2D on handheld versions and 2D/3D camera on console versions.
The game will be available on Wii U, PS3, Xbox 360, 3DS, PS Vita, PC, and next generation consoles (such as the Ouya for example).
The new Sonic game on the other hand will be different on one hand, because now when complete a stage, they will exits which will take you to another stage. They will be 20 different stages, not including boss stages.