I spotted the new demo on Steam and I gotta say, I've been pleasantly surprised! The fundamentals feel just right, the art and animations are lovely, and I enjoyed my time. I'll be keeping an eye out for the release to be sure.
Now, you did ask for some feedback, Beyond the good stuff, the text could certainly use a second pass, but you seem well-aware of that issue. With that in mind, the only real problem I had, and it's a minor one, is how the passages where you need the slide work: they're way too dang tall :D
Xandria could just lower her head a bit to get under these things, and I honestly thought I didn't understand the controls for a minute or two before I figured out what you were doing there. They really don't look like you need a special ability to get through them. There are also the bits where you stop the player sliding by putting a floating platform underneath them. I am not a fan of that kind of "gamey" approach that feels like it's exploiting the controls more than being an actual obstacle, but I think it's more a personal problem than any actual design issue.
I think it's telling that this is the biggest issue I had with the demo. If you got the basics so right a year and a half ahead of release, it's a good sign for the finished game to come. Keep up the good work.