There are a few recommendations I'll give for your game: Better player feedback, better visuals for the game, Make the player bigger, and make the player faster.
Better player Feedback: Small things like changing buttons slightly when hovering over them, or giving directional indicators when someone gets hit to know why they're taking damage aren't even optional. They're necessary. If the player isn't being told what's happening, they're going to have a harder time finding out, which can be tedious and an instant turn-off for players.
Better visuals for the game - you don't even need to do any extra art for the game. Just make a strict colour palette that's vibrant so that everything can be seen clearly without the colours looking ugly when combined or on their own. SuperHot is a good example of this. Very little art, but a really vibrant colour palette that makes everything pop. You instantly know what's good, bad, deadly, or neutral, without the game losing any visual quality.
Make the player bigger - I feel tiny moving around the place. Neon games usually give the player a sense of power or superiority, but playing your game I feel tiny and insignificant running around a really large and empty level.
Make the player faster - trust me, making any combat-related game faster than you initially intend is a really easy way to almost instantly make the game more fun to play. Especially with the neon theme, making players faster makes them feel more superior. Mouse sensitivity should also be considered.
Jonas Tyroller on YouTube actually has a few videos showing the fundamentals of improving fun in game design, and more often than not it's just really small details that make a huge difference. I highly recommend you watch his videos.