I got to the point where I'm getting +every material during fire, and i have 5 runes equipped. If you ask me what I would add, is maybe a way to move around in the upgrade menu by dragging the backround and a way to dissequip runes (haven't found out how to yet). I love this game already, but I'm stuck at the spot where I need Violet Crystal to craft a rune.
Overall an amazing game!