Just finished the game by destroying the orb and killing Zuggmoty. My team were mostly lvl 11 at the time. I found out a bug (or is it a bug) which made the game rather easy to finish. My Dwarven Cleric, lvl 11, had Laret's Staff of Striking and when I used the "Greater Magical Weapon" spell on it my Dwarf became a bringer of total doom. He made a critical hit to the guardian in the plane of water, dealing a 436 points of damage in a single hit and killing the demon. When not doing critical he dealed 190 - 230 points of damage. And because he almost never misses and strikes two times in a turn, Zuggmoty was killed in two turns...

Anyone else bumped into this?

Yeah, I noticed this too. Maybe it has something to do with the charges that are on Lareth's Staff?
Anyway, I just don't enhance this weapons, because it obviously isn't meant to be so powerful.