I love this style, the music and sound effects also fit really well. The inflation of the enemies is a cool mechanic, especially with the small screen size. It makes for some tactical decisions: shoot all enemies and get stuck with 3 massive enemies or focus on one at a time. Nice!
The shooting mechanic unfortunately lets it down for me. It feels very unresponsive. It's as if there is a specific cone in the 4 directions in which the mouse clicks get registered, but not outside of it. I have no idea if that's the logic behind it.
I think it would be better if it was only keyboard controlled. For instance, WASD to move and arrow keys to shoot.