Really neat little project!
Positives -
I feel like the boss works quite well for this example as it challenges the player without being too rough, allowing for them to get a good sense of how this engine works. I also like the physics for this and I find the spriting to be really well done.
Negatives -
The lack of music makes the game feel a little hollow. Additionally, I'm not a huge fan of the weapon selection and I find Quick Boomerang to be lackluster to use.
Excited to see where you might take this in the future. Also, what is the boss called (if he has a name)?