Oh my god!
I don't actually give 5-stars very frequently - but this was immensely satisfying!
I could complain about the length (or lack thereof), and that it is more of an extended tutorial / fancy toy than a full game... but it would be such an awesome tutorial / toy that I'd take this over a dragged-out, content-starved game any day - lots of awesomeness in a small package is almost always better than bloat!
The only issue I have encountered was this:
I once launched an enemy (with a combo ending in 's', I think) into the air, and it kept on going up, seemingly with no intention to ever come back down xD Luckily, I had full charge and used 'w' to catch up to it, which turned the potentially game-breaking bug to an awesome feature =9 It would have been bad if I did not have 'w' available, though ^^u