What's wrong with a world-class platformer?
The single best aspect of this game is that it combines a linear structure with plenty of opportunities to explore in many directions. The key is that one never feels lost. And just when you think it's a straight platformer, the game throws in a tough puzzle challenge to keep you on your toes. The control is also tight.
The two main drawbacks are out-of-place and annoying boss battles and the less-than-stellar save system, which can leave you stranded with not enough extra lives to give you a fighting chance.
I think this is just a great game.