The situation with "boss fights" in this version of the game is showing a consistent pattern: the party cuts through the dungeon in a reasonably efficient manner, only to be overwhelmed by the boss. In a few cases, repeated attempts at the fight have produced a hair-thin victory (the Quick Save/Recall function works wonderfully). In others, the group hasn't been able to win with any tactics.
This latter situation has been true (so far) for the Underground Fort, Spiral Fort, Island Fort, and the Hidden Aranea Lair (south of Lost Bahssikana). This could be a result of my party composition, my play style, design imbalance, or some combination of the three. It is interesting that, even though the party is now several levels higher than the original encounter, it is still being defeated in the Island Fort boss fight.
There have been several boss fights where, usually after several tries, the party has narrowly won with the last member still standing and just a few HP remaining. These fights are certainly rewarding and, to me, indicate a good, tough balance in the fight in question. That's as good as it gets, at least for my personal sense of accomplishment. The ones noted above weren't close.
It will be interesting to see if this pattern continues throughout the game.