As far as the writing in general, I thought BG2 was better. While I like the plot in BG1 well enough, I found Sarevok to be a generic, cliche antagonist. By comparison, Jon Irenicus is far more interesting and much less transparent. He's still one of my favorite villians in any crpg.
Sarevok was generic enough that I could pretty much ignore him, but Irenicus was one of those smug, super-awesome-to-the-max uber-villains that I just can't stand (actually, that's pretty much Dart's generic American TV-style again). Between him, the linearity, and the dominating NPCs, it's just spikey blue hair away from being a JRPG.