This game by Nicklas 'Nifflas' Nygren started as just an experiment to see if he could do a physics system really well, and boy did he ever; it's one of the funnest games I've played. I don't know if I've ever seen a platformer with such beautiful backdrops. Everything about the game-play, visual style and music (all these lovely low-key guitar tracks) are impeccable. One of the greatest 2D games of all time.