Good implementation of the theme ^^
The energy drain system is a cool concept, i just feel you went a bit overboard with how fast the energy drains compared to how much you gain back for enemy kills and the time it takes to kill them, the speed loss when low on energy also makes it quite hard to get a chance to bounce back with a last chance refill.
I don’t know how Unity handles this, but if possible i feel it would be better to not have interpolation on your sprites as it gives a very blurry effect on pixel art, and i’d say you could add a bit more feedback for enemy deaths like a small explosion or something to spice things up, but other than that i like what you did with the very retro arcade style sidepannels.
It’s a solid base keep at it :)