It's not enough that you put 'hints' in for Act 4. It's literally that you cannot adequately prepare for the boss fight in that little amount of time. It completely kicked my ass on Normal, even when I knew it was coming, because you simply do NOT have enough time to prepare for it.
I like it. Despite the Pay to win stuff tacked on there, I've had a good time so far. My first suggestion: fine tune the gold/shop system. Maybe put a refresh timer on the shop rather than changing after every battle? Several times I was only a few gold shy of a weapon I really wanted, only to have it disappear when I went into a battle to get the funds required to buy it.