Very cool game. I like how momentum and speed factor in the gameplay, it makes it stand out from most platformers. I also like the graphics and the music, simple while nostalgic, very reminiscent of old Atari games.
However, I want to point out a couple of glitches I found and a few things that can be improved.
On level 6, when I put all of the keys in their altars, the outline of one of the keys didn't change its colour, it remained gray. I assumed that I had missed one of the keys, so I explored the whole level from one end to the other before I realized, while passing by, that the door had been opened. I would recommend, after gathering all the keys in a level, putting in a music or visual cue that indicates that the door has been opened, in order to make it clearer.
On level 7, when I jumped into one of the floating platforms by accident, I ended up inside it and I couldn't get out. Because of that, I had to start the level over, losing my progress. I think that, on top of fixing that glitch, you should add the option to restart from a checkpoint in the pause menu, so that players aren't forced to restart the whole level.
Otherwise, it's a pretty good game.