Thank you so much for the detailed feedback! I'm really glad you enjoyed the game.
About the UI, it wasn't directly inspired by Shovel Knight, but more by NES-era games in general. Since Shovel Knight also takes a lot of inspiration from that era, I guess there is definitely some connection there haha.
The double jump and shooting mechanics are actually things I want to add in the full version! My idea is to create a progression system where players unlock new abilities based on their score, something like:2000+ score → double jump. 3000+ score → extra HP. and more upgrades as you progress.
I really like the idea of making the player feel stronger as they improve. I also agree that some enemies can feel a bit too fast, especially the slime. I'll keep that in mind and make some changes in the future.
Thank you again for playing and for the great suggestions!