you shouldn't really compare BG3 to BG2 yet. But as far as introductions go, the introduction of Irenicus and Imoen and dungeon crawl to the Promenade are head in shoulders above our brief jaunt through hell and all the vague Absolute stuff.
But I'm someone who still enjoys going back the BG2 so maybe my opinion is colored by years of hind-sight. I can't be really sure what my first impression of BG2's intro was, except that it was heady and made me want to rush through the game to save a friend from being tortured (I was a more naive gamer then). I'll have a better impression of BG3 when, or if, they make the tadpole into a more effective ticking clock.
I prefer BG1's intruduction.
BG2's assumed that you've travelled with this predefined partt (Imoen, Jaheira, Minsc, Khalid and Dynaheir) in BG1. Even if it happened that these npcs died in your BG1 playthrough, which is pretty immersion breaking right from the start, imo. And then they made Imoen a Bhaalspawn, never explaining why her essence didn't return to the throne upon death as with other Bhaalspawn characters, including the main one.
