Game has a lot of awesome things going for it based on the demo. I write this having played on PC so my feedback is based on the Windows Demo. If the full version has more features that render the feedback inaccurate please let me know.
Controls are smooth and responsive, soundtrack and sfx as well as visual direction is great. Bosses are very well designed and challenging in a fun way. This game has a lot of awesome stuff going for it and is very well done. I would highly recommend this game to anyone looking for a good metroidvania, I plan to snag the full version when I have a bit of free time to devote to it.
I say this because I have some criticisms which take up the bulk of my comment but they really are not game breakers and some of it can be very subjective.
One of the biggest points of Criticism is the save system being disabled in the demo especially given how unforgiving many parts of the game as well as the bosses can be. I am curious why the decision to disable saving was was made. Obviously the game is a steal at $2.50 and the demo should serve as a good taste of what to expect but being so punished for taking a test drive feels kinda bad vs limiting what can be played in the demo.
The lacking options on PC is also a big downside. You can't configure Keyboard controls though there is a controller configuration option and the only control you have for the visuals is aspect ratio. Unless there is a keyboard hotkey that is not stated in the description or in game there is no way to increase the resolution so expect to play it in a very small resolution on your PC, especially if you run 4k as at 1080p the display is very small.
I feel like the double jump system is interesting in that you have limited ammo that is used both to attack and for mobility. With that said, I feel that the jumps themselves for costing ammo are a tad punishing. When you reach the first spot where your normal jump is not enough, which great way of teaching mechanics through the game, the vertical momentum granted by the shot jump is so tight it feels like a massive resource drain early on. You can easily blow through all three shots just to make what should be a simple jump.
There are areas focused on the mechanic that I think are great such as the hallway of spikes you need to shot jump your way through but personally it feels a bit too punishing. Subjective feeling on my side but I think it would be nice if it was a bit more forgiving early on and as you progress the timing can get tighter.
Lastly, based on what I played, I feel that the introduction to the spike hazard could have been done better. When I first encountered the purple crystal spikes it looked just like a piece of level scenery to me and did not jump out as spikes until I was injured. As a stage Hazard it didn't really give an immediate visual indicator that it was a hazard and not just part of the level. It is far more obvious in later parts (like in the preview screenshot) that they are spikes but the first room I encountered the crystal spikes in just looked like scenery for the room.
Again, these are kinda nitpicky and the last two are especially subjective. This is a great game and I love what I got to play and would highly suggest giving it a try.