I really like the art style and the music is very funky and fits perfectly so well done! Already a really nice mix of enemy types that all feel different and the sound effects are good as well.
Some tips/ideas:
It would really help to have some sound for when your gun needs to reload because at the minute its hard to tell especially when you're in a battle.
Also I think making some distinction between levels like changing the colours slightly would give a good sense of progression. Maybe have some enemy types that only appear in later levels (pretty sure there isn't at the minute) so that the game gets progressively harder. Also perhaps a reward for getting to the next level like some extra coins or a coin multiplier as sometimes I didn't know whether to explore this floor or move to the next.
The guns seem to get a lot better as you upgrade which may mean the player finds the game too easy when they unlock them. To combat this you could make guns feel very unique and so some are good for certain types of enemies
That being said its still really good so keep it up!