So I've played this demo and for the first hour or so, I was quite frustrated with the game. Despite telling us it's an "open" game wherein you can choose where to go, going to Dungeon 2 before Dungeon 1 is borderline impossible to do. So my first savegame got stuck right there.
I restarted, went to Dungeon 1, then 2, then 3 and had a much more enjoyable time, all those little secrets to find on the overworld slowly but surely make you strong enough to take on the heavier dungeons, the fights with the bosses were fun, though I found the controls a little weird and hard to get used to.
Jumping is rather awkward and jumping from standing still vs moving making so much of a difference, I've very often jumped into things by accident because I had to make precise moves and just made a teensy mistake, hitting an enemy bullet of some sort and getting knocked back, my shield is useless as I blink in temporary invincibility after a hit, meaning if a bullet is IN me when I go out of it, I immediately get hit again.
BUT, I beat all three bosses and in general had a really fun time, I'd say the game could definitely use a dedicated map that grows as you move around, because the game is quite maze like and without an overworld map, it took me a loooong time to correctly remember the paths to various places.
The secrets were great though, when I found that spot where you can literally walk through the wall, that was a great moment and I hope the final version of the game has a whooooole ton more fun secrets to discover.
One final minor gripe with the game, is that progression feels a little chaotic, experience feels rather useless untill you've got a few items to speed it up, but even then it's basically pushing you to "grind" to get your health back, moving back and forth between screens to kill enemies, get health and progress further. This really is rather boring and I'd say that strategically placed health pickups would work better.
And that's that, I generally liked the game and look forward to seeing more of it!