This is insanely impressive for a 13-day jam game. Not only does it look great, but its very polished and feels good to play. You guys are a relatively large team, but still, the scope and quality of this are really good. I really like the open ended nature of it too. It's fun to explore the different areas and try to figure out what to do.
Only real shame is the lack of a real ending. Obviously its incomplete, but it doesn't seem like you even need all three artifacts to get it. I accidentally stumbled on it after getting the artifact that makes you float. I'm looking forward to what you add after the jam, though!