Wow, this is really impressive. The sheer amount of content (both graphical and gameplay-wise), and the fact it all fits so beautifully in 64x64 is amazing. I liked that leveling up helped you both in-battle and while mining (it makes you feel the upgrades that much more), and I think the core gameplay loop is rock-solid (pun intended). I think there's a lot of room to continue developing a game like this, if you decide to!