I havent finished the demo, but I have played enough to get an idea as a player seeing the game for the first time, think of this more as a "first impressions than a judgement on the whole and, if any points I make are solved later in the game feel free to ignore my feedback.

 Firstly the good things:

I think the combat is quite nice, has some real weight an impact on hits, and some good particle effects to boot

The art style of the world is quite nice, the particle effects, wind, beautiful vines and spikes, glow, etc, they all look great and at first glance the game looks quite well made.

Some feedback and things to improve on:
I like the art of the world, but the 3D characters dont quite mesh well with it. Of course you cannot remake them all in 2D now, but I would look into some Post Processing or any shaders that could potentially help make the contrast less jarring, having obviously handrawn assets right next to obviously 3D ones just doesnt look coherent.

Another thing about the art style, its very reminiscent of Ori And The Blind forest, quite intentionally so, however, this will no doubt make players compare the two games, and its not hard to see areas in which this game is lacking, I already mentioned the 3D models but also the nonexistent background. Now you for sure dont have the money or time to be exactly like Ori, but keep in mind people will compare the two, and try to not be significantly behind, otherwise why would somoene play your game and not Ori? For now anything other than a black background would really help aleviate some of that feeling.

Next, I want to talk about the world, as far as I got there was basically only grass, some vines and some wood in every room, it didnt really feel I had anything to explore, except more grass, vines and wood, you are also making comparisons to hollow knight and the world in that game is so amazing that if yours is largely empty it will really sour the experience for a lot of people (this problem might get better as it goes on and I just havent gotten far enough, but just saying). The world is one of the most important things in a metroidvania so yours feeling empty and not worth it to explore as it has nothing interesting in it would be very bad for the reception of the game.

Lastly, some slight nitpicks that made me frustrated in my time playing, but might be nonexistent problems for others or they might get fixed as the game goes on:
1 The first area has no map. This ties in with the fact that the rooms are quite samey so It was very easy to not know where I am in relation to everything else. Either give the player ways  and landmarks to understand where they are (ala salt and sanctuary)  or just give the player a map from the get go so they're not frustrated (ala Castlevania).

2. The checkpoing is too damn far back, the player walking speed is pretty slow and I have no idea where im going so dying and having to walk all the way to I dont even know where is really frustrating, making it easier to traverse the world, having more checkpoints, or again having a map would aleviate some of this frustration.

Hope I was helpful, and hope feedback from this demo helps you improve and end up with an amazing game!