Not bad for a demo. I liked how much detail you put into the scenery, and I could maybe see how some things could be applied for the final games lore/gameplay (such as the fountain at the start). As well as that, the speed of the character and the jumping felt grounded and controllable, which is a plus. Only thing I'd add, apart from just, more, would be a way to get to the main menu from the game since I had to press the windows key in order to escape. Knowing that this is just a demo though, you're probably already going to add that.
Look forward to seeing the finished product!