Yay! Thanks for playing and for the detailed feedback.
I really wanted it to be possible to play with one button, and the controls felt pretty intuitive to me but you never know how that's going to turn out. I have had a few folks not get that you can "paint" so I tried to just throw that language around in the mini-tutorial and on the itch page. I still need to implement edge-of-screen camera panning.
I had planned on an "upgrade ritual" for the towers that would use the crystal resource (if you happened to stumble on that deep in the mountain) but was nowhere near finishing it so it got the cut. And the metal ore used to be laid out in slightly more obvious veins that you might want to follow, but there was just way too much of it in the game so that got balanced out a bit. On the harder difficulties, you might want to micromanage a bit -- metal takes a long time to mine and if you go full auto you'll end wasting some time mining extra metal. I had contemplated adding a limit on the number of spots you could mark to mine out, but that feels like a bit of a shortcut/hack around the real issues.
I'll have to do some thinking about other tower types / ores.