I liked it! The art style is cute, and the amount of abilities is good (I believe there will be more, right?). Also I can notice that you have polished most of the things that are there, made with care, attention and passion.
There are some things that were a little weird, at least for me.
# The control layout. It's kinda weird to get into it. I suggest you to change from using a row of keys to something like two rows. You know, UIOJKL or something like that instead of FGHJKL. Also, Jump being the spacebar was a little weird as well since you had to change back to the other keys to do things.
# The wall jump. At least in this demo, it doesn't feel that useful. Also, I believe the character gets down really fast, so there's not a lot of time of response. Maybe this gets better if you change the key for jump.
# The cave layout. This is probably just me, but the square-ish approach (I understand) makes the layout feel weird specially in the thinner parts of the cave.
# The camera/view. Specially in the cave. You get to see a lot and since the character is tiny, it feels a little distracting.
I got this error while fighting agains one of the monsters on the cave. I believe I was supposed to die or something but I hope you get to find the issue and fix it.
I hope you consider everything I said, and some of those things are just nitpicks or my own point of view. Maybe you chose them in purpose and thats a way to see things, different than mine. You don't have to change them, but if something of those comments help, I'm glad I did.
You said you posted the demo to get feedback about how the game feels. So far, it feels good! But I believe it can feel a little better! I made a prototype for one of my games for the same purpose, but this is way more polished. I feel like I'm already playing the real thing, but I'm glad that we can help you to get other points of view!