I love this game's color palette! It's very controlled and eye-catching. Some of the enemy designs (like red the one that spreads bubbles across the level) were very creative and really made use of the game's bubble aesthetic. SFX and music also contributed to a concise, retro aesthetic. Not to mention the ability to aim in four directions made the gameplay feel flexible and controlled.
I did have a glitch where I fell off the title screen after jumping and falling through the platform, and then again during two later runs, which forced me to quit and restart each time. Though maybe that was because I'm on the no-Vsync version. I also think the controls might be smoother if Space was shoot and W was jump, since it feels strange to reach over to the down arrow to fire sideways, but that could be just me.
Otherwise, this is a very nice game. Great work!