Haha, the duality of gamers always fascinates me, as I was just sitting down trying to come up with ideas to make the game more intuitive and easier! I think really though, the biggest issue is that the difficulty curve is extremely steep in the first few levels, especially if you haven't learned yet how to play defensively (avoid making monsters upgrade that you're not strong enough to kill), but flattens out and becomes trivial in the late game after some hero upgrades.
Thanks for playing and for the feedback! I think I'll be releasing an update after the jam with some slight simplifications to the game flow, as well as a sped up and more consistent speed during turns.