This was so much fun !
Ahhh, the title is too long... more seriously, my only problem was the freezes. I'm pretty sure it's caused by some memory leaks.
For gameplay, it was just very fun, good mechanics, the game was easy to understand but has a high skill ceiling, very good. I took some time to realize I could double-jump. I don't think you should change the hold mechanic, because in this way, you should time your double jumps.
I think homing rockets became too powerful at some point, and there was no point in keeping moving, that's a very important thing to balance.
Mabye you can add a game over screen, I don't know if there is already a win screen.
Now, for the art, the thing you asked feedback on. I really like the current artstyle, it makes the enemies look alive. I think the main character needs more work. But most importantly, the biggest improvement you can make is consistency. You should try to keep a consistent palette (in a way to always have enough contrast between BG and characters). In addition the background's style was very different, it's good, but I think you should rework it. A good example of this is the title screen. Also, mabye add some particles like mabye tiny one when you jump, land, etc.
I think the UI can be more visually appealing, more juicy, more polished.
The music is just a banger !
Very good work, very fun concept. It is definitely worth it to continue working on. Good luck !