Hello, I played GumChu Girl's demo and since you asked for feedback, here is mine !
I really had a lot of fun, I thought the game was colorful, dynamic and catchy. I like that it is very simple (in a good way !) but still has a distinct identity !
The single mechanic works wonders as far as I'm concerned, it's very inspiring to see all you can do and all the interactions possible with just one move, and it's very very inspiring as a super-beginner game dev.
At first, I was a bit bothered by the fact that drawing the gum back prevents jumping and slows you (I assume it's to prevent infinite verticality ?) but by the end of my playthrough, I had changed my mind and found it rather charming. I like how it makes the game slightly slower, when most platformers nowadays are rather high-energy.
The music was pleasant and enjoyable, though for me it lacked a bit the genuine, original identity that is distinctive of the game's overall design.
Anyway, these were my thoughts on the game, I very much look forward to see how it pans out and I'm excited to play the full version !