Mark of the Ninja
Without any delay, I give it to you: Mark of the Ninja entered to my Top 10 Games of All Time. That is the how much I liked the game.
This beautifully crafted 2D action stealth game. You are asked to go through the stealthy approach in the entire game, but if you are more willing to make it a blood bath, it is a viable option too.
The controls are sharp and the levels are very well designed. And just like Super Meat Boy, the difficulty level is at the point that it you will get compelled to replay it for a better score.
Music is great, story also very good (makes you wanting to know more about the mysteries ahead). I got really inspired by the Klei production.
I played it until I got almost all the badges and challenges completed. When I finally got almost everything possible, it made me sad to uninstall it.