Cruel World (blame everybody else) is a neat concept for an asynchronous multiplayer game. The game launched with lots of checkpoints, but as people played they could claim ownership of these checkpoints, making the game harder for everyone else, and they can lay mines in checkpoints to kill you. Players can work together to hack checkpoints, in order to gain access.
The platforming itself is interesting and challenging. It has a unique platforming mechanic involving rolling and bouncing off of things that's hard to describe. It deserves a lot of credit for being a platformer that works differently than any other platformer.