Nice to see Takao back, and back with style at that.
Finally beat this game a couple of weeks ago (JP version), and loved it.
I didn't bother with all the challenges in the end, but I did all the story, DLC and the like. It came close to 20 hours of gameplay, but never felt tedious or slow. Collecting the gems and powering up reminded me of Crackdown. The combat system is fresh though I literally can't think of anything to compare it with.