I was 14 when BG1 was released, so both BG games are very nostalgic to me. That said, even back then, I thought BG1 villain Sarevok was fairly boring, a big dude in a cheesy armor with a "scary" voice while BG 2's Irenicus seemed far more interesting. Sarevok didn't really become interesting until ToB. And while both games have some memorable scenes, for me mainly BG2, I think PoE does a fine job at that too. Personally I enjoy every scene with Thaos, the first time seeing him activating an ancient machine, with no idea of what was actually going on other than some form of human sacrifice and then stumbling into a town where you are greeted by a tree full of hanged people. That really set a grim tone for the game, which I really enjoy. The slow unwrapping of Thaos plot is also handled well, rather than holding grand speeches to you, Thaos barely register your existence and you are somewhat left to piece the story together yourself in the first two acts.
While it's hard to say how much will hold out as memorable moments down the years, I have at least been impressed with the consistent good writing of both main and side-quests which I think is this game's true strength.