Really liked the pixel art. It's very well done!
The game is a bit too difficult in a way that doesn't feel entirely fair! The enemies that shoot at you can feel unpredictable at times, so maybe having some sort of indicator for the player that they're ready to shoot could be really helpful. The vertical movement feels pretty good. I'd recommend maybe playing a bit with acceleration and deceleration time on the horizontal movement, see if that's something you like!
I'm not sure if it was me but I didn't get any sound, so I can't give you a ton of feedback there :p
Keep up the good work!!