I’ve played through version 0.3.0 in its entirety. By the end, I had 151 copper, 4,552 tin, and 4,199 iron left over—that pretty much says it all.
That said, I think the game is heading in a good direction. I really like the lightning; the achievements are a nice touch (perhaps consider adding a small bonus for earning them), and the fortress, traders, and smelting mechanics—all great!
The bomb, however, feels a bit useless. It has a lot of health, but by the time its hit points are depleted, the lightning has already taken care of everything around it.
I also haven’t quite grasped how the "levels" work yet. But I do like the bosses—hopefully, there’s more to come in the future!