Really interesting mechanic covered in an amazing pixel-art, well done! The levels were very creative!
My only criticism is the complete lack of tutorial, I've seen many people do that. I understand the lack of time during the jam, but a little text box at the beginning explaining that you have slowing and accelerating bullets doesn't take longer than 5 minutes to implement. I know that this information is in the description, but the game should explain itself. Plus, by not telling the players everything in the description you can surprise them with new mechanics that appear later on;)
But that being said this entry is really solid and I enjoyed it!
Keep up the good work!