finished the game today, enjoyed it alot. Act4 was kind of a break in the pace (all that items, secrets and money felt useless because you could not leave), but i understand what they are trying to go for.
Warrior difficulty is great up to some point in act2, you are always barely getting by and always in danger. But that changes quickly when you manage to save enough money for good weapons and a few key spells. Lack of money is mostly where the difficulty was. Then its just facerolling. Dangerous caves are not dangerous anymore and require barely and preparation. Bladedancer pretty much walks over any foe and can kill common enemies with 1-2 strikes. The only skill i constantly used in act4 was regeneration and sometimes burning determination, other than that just attack.
I put a few mana items on my bladedancer for the heck of it and played with Carnage a bit, its devastating. And even more so with mandate of heaven. 2x Carnage was enough to kill everyone surrounding the party, but that was not really necessary, just saved some time.
If i play it again, i wouldnt do act4. It was not challanging, but long enough to become a chore. It's a great game up to that point though.