This was fun. I really like the concept and would love to see this developed further. If I could change one thing, it would be to have some indication of what the upgrade I'm choosing does when I'm selecting it from the chest between rooms. I can see the stats change when equipping the item I chose, which helps, but it would be good to know what is going to change for each of the choices I have before I choose one, maybe with a tooltip or something under the icon itself when choosing your upgrade.