Pretty good demo overall. The 2D-art is great (the pause-screen is amazing!) and the polygon models are pretty good too. The music is definitely the best part of the game, it perfectly captures the atmosphere you are going for.
I quit after dying twice, both times because my character got softlocked between two baddies attacking him. I feel that you should be more forgiving with your checkpoint placement, to prevent people from feeling like they lose a lot of progress :p
I tried out both control schemes, but neither seemed great to me. For the arrow-key layout, I found hitting the attack-button really bothersome and awkward. For the WASD layout, it really broke the flow that I had to take my hand of the mouse to do certain actions (unfolding ladders). A gamepad control-scheme would definitely be preferable, though I assume it's absent due only to this being a demo.
I'd also say that the game felt quite slow and clunky on the whole. It controlled relatively well, but everything just felt sort of off. Most of the animations could benefit from some touch-up as well, though I will say that the attack-animations were pretty great.
Combat felt quite one-sided. Either I would soft-lock the enemy or the enemy would soft-lock me, neither of which was very engaging.
On the whole though, you seem to be going in the right direction. Good job and keep it up! I look forward to seeing more of the project.