arken

I own and have played all the games listed, my favorites being Arcanum and Baldur's Gate II/ToB. While I would have to say the appeal of Baldur's Gate and Arcanum are the biggest hooks for me, but the OUTSTANDING story and setting of Planescape: Torment could easily be seen as "at least" a big of hook as BG/Arcanum, as my personal preference is that PS:T had the best overall story than any of the games listed. But seriously though, all those games rock.