Been following this project for a long time now and I just played the demo. Here are my immediate thoughts.
Some issues I have so far with the gameplay itself is the spawning system for enemies, they can spawn very close to the room's entrance so when you walk in you are instantly in danger, placing enemies further into the rooms would give you more time to react and would be a welcome change.
You also get no I-frames when entering a room which would be no issue if enemies didn't wait by the entrance after you leave the room. I would highly recommend rather than enemies dying and being deleted from the world you look at the legend of zelda series and instead set them to be invisible, inactive, and back to their starting position and upon reentering a room they are set back to visible and are reactivated. If you want the rooms to be random you could take the isaac approach and handmake many rooms with predetermined enemy and trap locations which can be placed in the world at random.
Slime knockback is also incredibly high and can send you out of the room which is a major annoyance. Slime should also indicate where they wish to jump more clearly and should have a sort of wind up animation. When they split they can also land directly on you and you take unavoidable damage.
Crabs tend to kill themselves with the water which is odd.
When you die you respawn at your current position which lacks any sort of punishment for mistakes, I would recommend going back to the world spawn or having spawnpoints spawn through the world.
Chests should be visible before defeating the enemies to incentivize them to stay and fight rather than to go to the next room.
As for bugs I have experienced a few, one major bug is the shell bug, if you pick up a shell and walk to another room it will float way ahead of you. There seems to be Z-layer issues with enemies in grass or that may be intentional?
I have seen numerous tileset bugs in the forest area in particular
What I liked, the UI is charming, the graphics are enjoyable. The concept is very interesting and multiplayer would be especially fun.
These criticisms are to improve the game, I want to see this game succeed it just needs work at the moment.