As a huge fan of metroidvanias, everything in the demo seems very promising so far. Looking forward to the full game!
I only have three suggestions;

1) Jumping feels a bit floaty and was too far removed from real world physics for my taste.
I think getting the jump to feel right is one of the most important aspects of a game with platforming elements since it will be the action performed most often. Please consider tightening it a bit more.

2) Please try to shorten the time for getting back in the game after death as much as possible. For instance, you can make the load animations skippable.

3) Please provide various pins to mark points of interest on the map and please don't lock them behind in-game purchases or unlocks. Ideally, we should be able to put as many pins (with different colors) on the map as we would like. Extra points if we can also attach notes to them. Otherwise, we would be forced to use pen and paper or a note taking app which breaks the fourth wall and takes us out of the game.

Keep up the good work. I'm sure this will be a big hit when it releases.