My favorite 3D platformer. When I was a kid I couldn't get past the first world, this game was just too hard, but as an adult the challenge is just perfect. I also love the ability system, it gives you so many perks and options in combat and losing all of them makes dying PAINFUL. Imagine that, having stakes and punishment for death.

It's also just the right length, long enough to feel like a proper game, but not so long that it's not repayable. Going back and replaying to find all the treasures and abilities is a blast.