Baldur's Gate 2 - while I really like both KOTOR and DA:O, former, while thoroughly enjoyable, is bit too linear for my taste, and latter is very good, but not as good as BG2, as a classic iso-CRPG.
Honestly, I was never big fan of Bioware - back in those days, I really liked and played them, but generally speaking, games that golden generation from Interplay made (including studios made by ex-Interplay folks, Troika and Obsidian), always resonated much more with me than any of Bioware's stuff.