If there's one thing that makes a story great, it's the characters. Baldur's Gate II had tons of unique characters, all with very fleshed out personalities. But one thing that made it a "Quantum Leap" was the integration of these personalities into different situations. Your stoic Paladin buddy may react differently to the horrors of a sinister cult compared to your brooding Drow cleric. And better yet, they may just react to one another, leaving it up to the player to settle their dispute. On the other hand, the game also offers the player a chance to romance with certain characters in the game, a relationship that grows over the course of the adventure, so subtly that the player may not even notice he's in that character's "romance" string.