Very fun game with a very unique premise! There is definitely a lot of enjoyment in trying to figure out the order to take down enemies and getting into the risky state of having to kill someone to regain health after getting smashed against a wall.
While it's definitely a game with a mess ton of polish in its visuals and juiciness in its movement/mechanics, I think this is the type of game that'd benefit from going almost overboard with VFX and UI animations. Like having larger explosions when an enemy gets splatted against a wall/firing a huge weapon like a shotgun, or colorful text VFX that appear after an enemy dies. Using warmer colors so they don't get in the way of the visual clarity you have from having your characters be black and white, while also still staying within the color palette of your environment. Also, definitely something when you get a combo higher than, like, 10 that's making everything super intense on screen. Something that's making you feel like you're doing super well without looking at the UI, since if you have a 10x combo, you'd prefer to look for more enemies rather than at the combo most of the time.
In terms of sound, having more sounds when enemies die, when the combo meter hits past a certain point, etc. All to contribute to the insanity of being a Roomba on a rampage type deal. Also, sometimes the music doesn't play when you die and restart a level, but thats prob a small fix!
Def a lot of potential with this game! Really nice job!