Well, the best way I have to describe the game is "Super Meat Boy meets Portal" aka "Reach the chamber exit fast and without dying". Sounds easy, uh? It is! Except for traps, lasers, lava waterfalls and the ever spinning saws. Levels are designed to kill you (and they will, often) and you'll find that the only way to reach the exit door is to exploit the level itself with a sequence of running, jumping, wall grinding and wall jumps.
Dark chambers redesign, ghost players in Training and lot's of other improvements :)