Very cool and satisfying game! Killing enemies really gets addictive as you become stronger, which is typical of bullet haven games, and the music is fitting too, so you nailed the game feel perfectly! I think part of the merit goes to the large amount of assets you used, since they basically give you good game feel and juice out of the box, but you also played a big role in assembling them together to provide a traditional yet compelling gameplay loop, so the game was nicely assembled.
A bunch of suggestions and problems for the game if you'll find them useful:
- Make enemies have different colors or decorations, because as of now, you never know if you are going to one shot an enemy or if it has a lot of HP, and this means that if I am surrounded by enemies, I never know if I can slice through the enemies to kill them all and not take damage while I move, or if they'll take more hits to kill so that I should not even try to move towards them to then slice through them);
- The music feels energetic and fitting for the game itself, but the upgrade sound sound effect feels off compared to the tone of the music, I think a quicker sound would be better instead of a melody for level ups;
- I feel like the pop-up window menu to upgrade tour stats is not really a good idea, a "vampire survivors" like upgrade system where the game pauses to let you upgrade your stats in between levels, or even having upgrade buttons always visible on the screen (with an hover tooltip to show you what each button does) would be a better fit for the game;
- At a certain point, about 5 seconds after you start playing basically, you can stop moving entirely: this is because if you leave your upgrade menu open and stay still, upgrading one of a few sets of stats is already enough to arrive at a point where each enemy dies before it can even reach you, so there is no need to move at all (and thus no need to upgrade the "movement speed" stat either); this may lead to a pivot in the direction of the game, instead of having a bullet haven similar to vampire survivors, maybe try to develop the game more towards the direction of "Heretic's Fork", with a fixed tower at center and enemies coming all around it;
- Also connected to the fact that at a certain point enemies cannot reach you anymore is the fact that the game difficulty doesn't scale properly with the level of the player, enemies do not increase, their health does not increase, and the game becomes easier and easier with each level up, until it stops being challenging at all (I got to level 250 without moving bt simply leaving the game open after upgrading basically everything to the max); maybe consider adding stronger enemy types spawning later on, or maybe enemies that shoot bullets that you can't destroy with your blades if you want to keep the player having an excuse to move on the map, or maybe add bosses spawning from a certain wave on;
- You can phase through elements in the game, and enter blue boxes and also exit the map (which makes the camera infinitely zoom out) if you keep holding the movement keys, which I believe was not intentional...
Ultimately, the game is incredibly addictive, polishing it a bit and deciding in which direction you want to expand the game further (either a vampire-survivors inspired or heretic fork's inspired bullet haven) would make for an even more addictive game, so good job :)