The demo is fantastic! I love the movement and puzzles, but you really nailed the environmental design as well. Everything feels very cohesive!
Personally I'd love to see some different sound effects for the NPC dialogues, but maybe that's something you had planned already :D
I was also thinking it might be nice to have a bit more indication on when you should drop objects for objectives. Maybe like a lil UI bubble appears when you bring an item over to the NPC/Puzzle to show that you should drop the object now. But that's just a minor thing and the gameplay isn't heavily affected without that.
Overall the game is shaping up to be amazing! Can't wait to see the other environments and characters you'll get to meet. Keep up the good work!