This is a pretty interesting game and I really like it. I didn't really find anything wrong with the game, but I do have some suggestions.
I think it would be more fun if the player character was a little more responsive. Maybe a dash move mapped to right click and a larger hitbox for the sword. Or maybe just give a little more space to work with, so I'm not constantly surrounded by enemies. You can always increase difficulty by spawning more or tougher enemies. I just feel like games are generally more fun when the difficulty comes from the enemy's power or numbers rather than my character's limitations.
Regardless of my game design advice, you should really implement a timescale slider when you're testing this kind of game. When I made a twin-stick shooter, I found it really helpful to play the game at 10% speed to see exactly what timing I was requiring of the player and how much room I was giving them to execute moves.
Anyway, really nice game. I just feel like it would be more fun if it had that bullet-hell feel of barely squeezing past a wall of projectiles. Some of those give you a 1 pixel hitbox and they're still really tough.