The quick verdict is that despite some nitpicks, that I am incredibly likely to back this project when it launches and to encourage anyone of similar taste to do the same.
Yo dude! Thanks for playing through the demo! You found everything too. Well, except for one chest, but that one just has more coins in it.
Thanks for all the feedback, I'm thinking about reworking climbing so you don't fall off the sides or bottom - you'd have to jump off instead (down + jump to just fall off).
I might rework that long sequence in the crypt as others have criticised it too, or at very least add a "look ahead" feature like the binoculars in Celeste.
The full game will feature button remapping too, for both keyboard and gamepad. I personally always play gamepad, so a good default keyboard layout is not something I really have a clue about.
Thanks again for the vid!
-Dan