I've just finished the game and was curious about this. Compared to when I had first played BG some 15 years ago, I died a lot less and leveled easier because my knowledge of D&D and tactical aptitude is now vastly superior to when I was a kid. For example, using all the proper weapons for each character, kiting enemies like wolves, ogres and bears, learning to instantly pause and jump spellcasting enemies with quick spells/abilities to interrupt them before they get off a horror/mirror image....
... however, on boss battles I died a lot more than I remember from 15 years ago. It was crazy. That guy in Nashkel swarmed me once, ok. But Davaeorn caught me in his instant-lightning-bolt several times, wiping the entire party. He was also surprisingly resilient. The battle atop the Iron Throne was also very difficult, with at least 4 casters throwing save or lose spells at me. The party at the beginning of the Undercity with their crazy mages and archers that shoot bombs - I had to reload at least 10 times, don't remember that from before.
When Sarevok revealed Tazok, Angelo and Semaj (the latter two being full of contigencies and the room's traps being undisarmable), I was like "WTF". The amount of spells that rains on you the very second the battle begins is insane. Sarevok also seems to attack faster and deal a lot more damage (which is way more dangerous than high magic resistance he had before). I probably had to reload the final battle 20 times. And that was after stuffing each character with every kind of potion and scroll known to man! I feel happy but a bit sadomasochistic after that battle. Were they really made that more difficult or I just have a rosy memory of the past?
Anyways, is there an official list of changes in comparison to the original game somewhere, like a BG to BG:EE complete patch log?