Chester is a 2D platformer with over 10 unlockable characters, a light RPG element and leveling up system, loads of unlockables, around 50 levels, and 8 "styles" that allow the player to change the look of the game at will. These styles include sketchbook, 8-bit, LCD, blueprints, and many more. They also each give a unique gameplay bonus to the player. The game also includes 4 difficulty levels so that almost anyone can beat the game or get a very challenging experience out of it.
http://www.desura.com/games/chester
Quite well-paced platformer with its own twist on environmental change (which is optional). You can switch between these modes for small bonuses, and they even change the art style, depending on the mode.
The developers are doing this as a way to have publicity so the game can go on Steam via the Greenlight system.