Not bad, but not my type of game.
It starts off really slowly, in my opinion. As others have said, the need for perfect jumps to get pixels gets extremely frustrating, especially when it's at the near start of the game.
There is no difficulty gauge, it just seems like the same thing as from the start with more abilities. At one point I glitched next to a wall and could fly again (When you have wings) to get more pixels, though I eventually just lost interest. Part of that was the spacing of the pixels and the lack of variation to get said pixels. Also, if you fail a jump you have to track back a rather large distance considering the speed of pixel character. These things to me aren't skill or mentally challenging, but rather just nuisances that could've been addressed so the player can focus on the actual content of the game, rather than waiting to go at it again.
The music was nice and surprisingly not annoying to me. A recommendation I would give is to make some sort of mini map that would highlight the remaining pixels that you are able to get and mark them a certain color, like yellow. That way there would be no confusion on where to go or on what pixel not to attempt to get.
All in all, it's not bad but loses it's "flavor" quickly. Leave a pixel behind, and it might take a long time to remember where you left it.