good game
I'm not the sharpest puzzle man around so I can't claim to have finished any of the Hard levels super quickly. Still though, I think it says something about the lack of difficulty if I saved the Easy levels for last, just to complete all the levels. IMHO the game could've been better if it were more challenging, maybe adding something like the ladders giving out over time or windows moving around in certain patterns. Only some of the latter stages in Hard were anything that taxing.
That said, the controls are extremely responsive and sharp, and I don't mind the music at all. In fact, it fits the game very well. If there were more variety to what you could do, maybe in terms of different power-up abilities that lasted for a set amount of time, or objectives in stages besides getting to the exit (the ninja's ability is a lot like Mario's in Sunshine, so why not some side objectives like cleaning up fussy walls or w/e?) would be nice for longevity.
Maybe some sort of multiplayer mechanic would be nice too; this is too fun a game to play solo, even if that means adding in (decent) AI bots :)