It was incredibly brutal. Pretty much your only hope of surviving is casting Mogato on Despairant (which instantly banishes it back to Hell--if you hit with it), and Labadi on Scaly Empress (which reduces her down to 1-8 HP, again, only if you manage to hit with it). Then, you have to hope, nay, pray, that one of your other characters manages to hit her with a weapon or spell to knock off that last little bit of HP. Did I mention that you pretty much need to do all that on your first turn, overcoming their insane ACs and Magic Resistances, before they get to act and (probably) annihilate you (their breath attacks alone tend to do three figures worth of damage, 200+ is not at all uncommon)?
The really bad part is that I had to fight her twice--the first time I beat her, my inventory was full, so I couldn't get the Empress' Scale item.
Needless to say, every boss battle on the last level is incredibly unfair--the programmers definitely went way too far/hardcore with the final level of this game. I imagine your average gamer would give up in disgust/frustration pretty quickly.
On another note, I updated my Wizardry III bestiary to include the more detailed stats from that Japanese Wizardry site, as well as a new sub-section for the ten monsters that aren't in the Famicom/Super Famicom versions:http://kramwartap.fortunecity.com/wizardry3_bestiary.html