Apart from the missing tutorial (my solution was to simply click everywhere), in my opinion the text on the signs (before purchasing the various camps) was a bit hard to read.
For balancing I never managed to get to the souls before winning, and the (dark?) gems were way to abundant.
I noticed either two bugs or one bug and an invisible mechanic:
I purchased the town spell but got the enervate heroes spell (though I am not sure if that is only visual, as I won the round after), and I noticed that the spell cooldown was not always accurate, without purchasing the druid upgrade to shorten the cooldown. Not sure if that was some hidden mechanic or simply some bug. On the other hand: "It's not a bug, it's a *feature*".
I would have loved to have some music in the background, but I really liked this game and might play it a few times more, trying out different strategies.