Like art in main game, somehow upgrade menu art like much less.
I wish upgrades more often change my strategy. It probably changed only once when I unlocked archers. I discovered myself on level 4 just spamming q/e.
Also wish to have different strategies in general. As long as cost rises so much there is no point for example try to hire only knights or only archers. So the only strategy is to press q/e and the only real gameplay after several attempts is only choosing upgrades. Probably you have to rethink gold and hiring econmy. If you need professional math support - write to me:)
Good luck with further development!