I enjoyed the demo quite a lot! At first, I thought that the side image was going to block a lot of the visuals when fighting (as a lot of games do), but then the camera zoomed out and I haven't felt so much freedom to see the boss fight. The art style is really nice and the world animations feel smooth. I look forward to seeing the game in its full release (I saw that pressing shift lets you switch weapon types, so maybe we can get one that launches a very very balanced and totally not lethal giant explosion?).
For the character model, moving her in any direction feels very stuttery, although it doesn't seem to affect gameplay. She also moves noticeably faster in the diagonals, leading to cases where it's better to mash the adjacent keys to improve mobility. A question is have is if the top part of her model counts as her hitbox, or if it's just the shadow on the ground?
A complaint I would have in terms of the demo's balancing is that once you're hit by something, there's zero time to recover/avoid damage. Perhaps down the line, there's abilities or passives that provide i-frames, let you dodge, or recover hp/lust?
Another (much lesser) complaint would be that the first boss fight, although the small targeting tentacles are easy to dodge, don't have any existing animations to indicate they are coming and will catch you off guard, especially with their color blending into the areas around it.
An issue I found is that for the first boss fight, if you put yourself right at the activation point of the boss, it'll spawn the boss, but the fight hasn't technically started, although it does zoom the camera out. Its health bar also isn't present, but you can still kill the boss anyways. It's possible to do this from any point of the stairway, so long as you avoid moving forward beyond the moment the boss activates. You can actually go left or right and sit around doing nothing in the boss arena until you move forward or head back to the center and start the encounter.
For the second boss fight, if you try to use the same tactic, the fight starts normally and you can see the health bar, but when the boss does his attack that sweeps half of the arena, it can force you out of bounds into the area behind it, and while he is still capable of attacking, if that same attack forces you into the lava behind and you recover in time, it puts you so far back that he stops attacking.