I'm currently playing with QuestPack v3 beta2 on my BG2:EE run. I've just encountered the lich Nazariel and my character (a Stalker/Cleric) was able to defeat him and his simulacra very easily without any help from my party members. The reason lies in his spell selection which seems to be limited to damage dealing spells. Since my character is equipped with the Cloak of Mirroring, I'm protected from all of his attacks. I'd suggest to give him a few disabling spells as well.
Finally, I haven't found any problems in the quests I have already finished (Besamen, Infernal Thievery, extended Reynald sequence, Sanik) and the AI improvement of beholders and illithids make the battles in the Underdark much more challenging. Although the increased number of Elder Orbs in the Underdark's beholder lair were almost too much to handle for my party.