The core mechanics in this are really solid, and it's a great example of easy to learn and hard to master. The controls are really simple (in fact, it could be played on an old Atari joystick if you were so inclined). The game will tutorialize things pretty well and then mashes things together and complicates them as you go.

Pros:
Gorgeous
Great music
Love the audio cues before each thing (that fit with the music)

Cons (for some):
Can be visually tiring
Can be very demanding - will punish you if you're not there in the moment

Nitpicks:
Had crashes changing resolution, then the game wouldn't start. I deleted and redownloaded it and everything worked fine (including saved data).
The mechanic where 2 fast up+jumps make you stay in the air longer is not obvious. If you are trying to get an S on 6-1 and can't get everything in the air, this is your problem.
Last 2 levels don't have the same feel as the rest of the game. They aren't that hard though, so I can overlook it.
The blocks with the green trails don't seem to behave differently than normal. I'm still not sure what they're there for.

Overall I'm really happy with it. I've 100%'d it (which is tough, as of right now only 0.4% have) and I'm actually a little sad as I'll not end up playing it much more. Highly recommended.