Got 1272 points :D Pretty addictive, had to spam space bar to make me stop :P
Theme:
Superb approach to the theme, you can definitely feel how intense the game gets when there are too many boxes. Good job :)
Visuals:
Simple, but clear and you did some polish like particles, so that's good :)
Actually not sure what to add, maybe some post processing would make it more graphicly appealing.
You can also try to change on the style and do something more glowy. So that all the cubes have their color, but they got emission material attached to them. It could also look nice :)
Innovation:
What a cheerful idea. I've seen many color related games, but this one really got me. Great experience.
SFX:
Also simple, but very well made, both sounds and music. Ear-catching definitely :P
Gameplay:
Fun, no bugs. A lot of variety and requires thinking, what else you need :)
Game Design:
Also pretty good. I really like the tutorial (having a preview of the mechanics there is a great idea!), you really need to learn management to get into the rhythm and ye, I love the option with space to spawn, really helpful.
Maybe at lvl 10+, 20+ etc you could add something that was in Tetris, so that boxes are spawned quicker and music speeds up a bit, so that you cant play this game forewer and it gets intense ;)
Anyway, amazing entry! Good job