It's clear that some good thought was put into the level design, and that made it feel very polished. I also like that you added a knockback when firing. There were a few areas, like a small moving platform over spikes or having to keep your timing jumping over bubbles while clearing out an enemy on a higher platform, that were made significantly more challenging where you could otherwise have essentially kept the fire button held down and breezed through. Felt very much like a Super Meat Boy kind of game, where you had to keep going through the level and dying farther along each time to finally go 'OH!' and string it all together. Very nice game!