My own experience led me to see that the game balance on Balanced Mode is generally good in Acts I and II, but Act III tends to either be too easy or a knock-down, drag-out fight and it would be nice to see something in-between.
I think the balance tends to favor specific party make-ups (in fairness, so does the D&D system of combat). In general, I would think the difficulties would follow the following idea:
Story Difficulty - Should be able to get through almost every fight with a suboptimal party without having to reload.
Balanced Difficulty - May need a generally balanced party to get through fights, and major fights may require some strategy to avoid reloading.
Tactician Difficulty - Will need a fairly optimized party to get through this without reloading. Major fights will require strategy, and may require reloading even still.
Challenge Difficulty - Every fight may require optimization, and major fights require significant strategy to present a challenge.
There isn't a "Challenge Difficulty" at the moment, but it sounds like there are some who would want such a thing. So if we go by those definitions, I think Story Mode could be generally set slightly easier than what it is, combats in Act 3 could be rebalanced slightly for more consistency on Balanced Mode, and I don't really have much to say on Tactician and beyond.
