Learning how to play is straightforward. You move. You attack. It's simple but it works. Let's you get right into the action with no friction.
More feedback on hitting enemies would be good. They bounce back and flash red which is a good start. Maybe they could play an animation, or some particle effects could trigger, or a satisfying sound effect could play. Something to make killing enemies more satisfying. Right now, hits don't feel impactful enough.
I like how the yoyo lingers longer as you move away from it. I think it would be cool to lean into this. Like maybe if you run away from the yoyo as its coming back and you don't bump into any enemies, it can hit multiple enemies on its way back to you or something, encouraging good movement and positioning from the player. Just an idea :)
Which gets me to my next point. I agree with VSI Games that enemies are too hard to kill right now. You could make them initially weaker and stronger later, or you could give the player more options on how to defeat them. You could implement something like the lingering yoyo mechanic like I mentioned before, maybe a way to charge the yoyo by holding the button for a stronger attack?
Overall, nice job on the game! Adjusting the difficulty and player options would make it even better.