Okay, there's so many levels, I'll stop here. If this is what you call a demo, I can only wonder how expansive you want the final game to be! Let me give you some of my thoughts:
-I like the ambience and the soundtrack!
-I wish I knew what I'm actually trying to do in this game
-You *really* should add checkpoints, given how long the levels are, and there are sections that involve pure trial and error, I don't think i should be knocked all the way back to the start of the level for a death.
-Every level is aesthetically pretty much the same except the scenery slowly changes, which made me feel like I'm hardly making progress. I don't think there are enough unique landmarks to invoke curiosity.
-Also, I picked something up? And I think it did nothing?
In my opinion, it can be promising, though I'd say try to just refine and polish your game now because you probably already made enough levels lol