The final bosses of BG 2.5 was impossible for me to fight. "My weapon has no effect."
"My weapon has no effect."
"My weapon has no effect."
I've got only one character with a +5 weapon, everyone else had trouble finding better than +2. Holy christmas, Jaheira can't use anything better than a club or staff. There's like nothing better than +3 for either that I came across. Fighting that battle felt like the designers were calling me on the phone just to personally insult my mum. And half the enemies spawned by the boss resisted every spell that Edwin, Viconia, Jaheira, and Imoen threw at them. And the fight lasts as long as several boss fights with no resting, so those spells are never coming back anyway.
Maybe I'm completely terrible, but the game makes no effort to teach you how to get around that crap. You have to search internet forums for cheese that you won't know unless you're already intimate with D&D 2e.