Not bad at all for the start a rhythm game, the concept of rhythm fights is cool, but as you also know, the timing is not on point (maybe you should check if you are using deltaTime correctly), the "charting" (how you design the notes to hit for the player) needs some work too (avoid long pauses when you don't have to press any buttons, and also avoid notes that are very close to each other at least for the start of the game to keep the difficulty of the game, and eventually of the levels, consistent).
As you know, the theme was not even considered for this, but I still want to give you some suggestions to improve the game:
- Make the indication for when to attack (and how to attack) bigger instead of having a very small text at the bottom left of the screen;
- The game starts with SFX volume disabled: I don't think this is something you want by default, since sound effects add a lot to the game, especially if it is a rhythm game, they could be satisfying to hear for the player and make the game feel of the game even better;
- Make it clearer that you are pressing the buttons because you are blocking attacks and then also attacking yourself: the idea of a rhythm game centered around boxing is very cool, but right now, with how the scene is presented, it is not very clear if this is the case (is it?);
- Add options to rebind the controls (I would prefer playing with other buttons for example, instead of up and down, use left and right arrows, or A and D, or even A+S+D and J+K+L like most of the 2 buttons rhythm games).
The game has its charm with in the artstyle, and I think you could even go for a humor-centered funny rhythm game with the same artstyle, like the game "Parappa the Rapper" for example.
Overall, I think this is a good start and a good concept for a rhythm game, keep it up!