It's a great game, even as a concept. The gameplay is very enjoyable, aesthetics are pleasing. Dashing mid-air until you run out of “stamina” is a cool concept. And I loved the tutorial with the ghost clone of yourself showing you around.
I probably missed a couple of optional areas since the road I chose seemed to be the correct one to reach the boss. I was wondering what the flames you're collecting actually do, since I've had a full bar for the latter half of the game. I passed it to the tree (?) which recoloured my animations but I still don't really know what changed (was it a damage boost of some kind?).
I'm glad for the checkpoint system, and it's placed very well so the game never becomes frustrating because later on, it's quite easy to die with all the floating danger and spikes. Even the boss's health is saved. Death traps send you to the last safe platform, too.
The boss himself seemed more like a challenge during the ascent, the actual boss room was very easy. As long as you keep moving, you're invincible, and the boss doesn't change tactics, so it's really about dashing up to him a few times and he's done for.
He's a giant skull; I'd add a few directly damaging attacks aside from the exploding skulls you've already seen.
Yeah, the no sound/music is a shame, and would definitely be my number one complaint if this was supposed to be a finished game.
It is a very good game in all regards, I'm excited to see where you take the concept.