This isn't really that bad, all things considered. It's slow, but considering it's a demo and you don't intend to make anything big out of it, I'd say it's pretty good. You did a great job with recreating the environment of Hollow Knight in a 3D space, and the atmosphere that you made for it was also very well-done. The music and the tone fits in well with each other.
Some small things that I found a little bit cumbersome about it is how the character bumps into objects and stops moving entirely. I think it would've been better to have let the character slide off of them rather than completely break momentum. Another thing that bothered me was how slow the attack button was--I think having a shorter cooldown time would be a great idea.
The camera was a little iffy to me at first, but I quickly got pretty used to it--the set angle that it's at is a really neat nod to the original game only remaining 2D, and I feel like it fits the scene pretty well.
The models also look pretty good, too--as does the environment. It doesn't look like the elements were taken directly from Hollow Knight--it looks like they were hand-made in a 3D software, and that little bit of effort is super neat.