The hooks of Baldur's Gate 2 for me were Minsc and Irenicus. Irenicus just has that classic villain feel to him that's not too cheesy, but keeps him memorable. Minsc is funny and I feel everything needs good humor.
The hook for Torment for me was the writing on your back. You're no farmboy out to save the world, you're just trying to get some memories back using clues scrawled into your own flesh.
I don't think this discussion should be limited to CRPGs. Just so long as we don't get confused between games we like for reasons other than story that attempt a story and games we like for their story. It's a harder distinction to make than it seems.
The game with the absolute biggest hook for me was Xenogears. I've raved about it in multiple threads, I rave about it practically every chance I get. My personal photo is a major character from this game. The hooks for me in that game are nearly countless. My first hooks were the mingling of sci-fiction and more traditional fantasy. Your character starts off little more than a simple youth in a village. Then the giant robots appear and start fighting each other! Then a mystery begins. The way the writers weaved Christian Gnosticism, science fiction, fantasy, and abnormal psychology into a unified epic really appealed to me. The stories that appeal to me most have a depth of well written backstory and I would be challenged, and challenge others, to find one with a deeper backstory than the one Xenogears presents. It goes back nearly to the dawn of human life on that planet and still feels personal. Because the back story of the hero, heroine, and villain reaches that far back without turning into a prophecy.
Despite the wide spread of opinions of the game, I also include Final Fantasy VII in my games with a great story. The back story may not be as deep as Xenogears, but it is deep. It also breaches into abnormal psychological considerations. Many games are satisfied to simply define a character's personality. Final Fantasy VII and Xenogears actually give explanations for why the character is how they are and they do it beyond the cliched conventions. Sephiroth is arguable in that regard, but Cloud I would never consider that way. He's a character whose personality was all based on a lie he convinced himself of.