Congrats on your first ever game!
I enjoyed the premise of it. Less health for more speed is something I did in my game too. I like how you had to gain enough speed to break through some walls in the game, I felt that was really clever and a nice twist on it. I also liked the animation on the cube, how it would close it's eyes if it was flying by very close to spikes, that was a nice touch.
If you wanted to improve, the indicator to fire was kind of glitchy, sometimes it would bounce off of walls, other times it would just phase through them, it also didn't show up when on breakable walls for some reason. Some sort of tutorial would be nice, even text on the background of that first level would help.