The game is pretty good, it has a lot of potential, and this little demo was fun, I even wishlisted the full game on Steam. But, I do have to point out some bugs:
Some of the sprites didn't load in, resulting in the enemy being just a black square. This made some combat encounters a bit tricky.
Enemy hitboxes were a bit weird, so sometimes I couldn't hit enemies unless I hit them at a very specific spot and sometimes I couldn't even hit them at all.
During the first boss fight, when I died and should've respawned, it didn't respawn me and I could just do nothing as the boss attacks me while I'm already dead, resulting in me having to go back to the main menu and resume. It happened again though, so at that point I had to start a new game.
I didn't see any other bugs apart from the ones I mentioned. All in all, I think this was pretty fun, although it has more bugs than the old Gamemaker demo did ( yes, I played that as well, back when it was released ). Can't wait for the full game to come out.