Mindbending and creative. Improves upon its predecessor in every way.
Despite this though, I would gladly take this title over its predecessor any day. The first one was a fun game, but it was attached to a fairly generic storyline anchored by an extremely overrated lead. As a life long fan of the Star Wars EU I loved how The Sith Lords tried to deconstruct everything I've come to accept about this universe. I'm not normally a fan of things that try to be "darker and edgier" but the darker tone of this sequel definitely helps out its forbidding storyline. Unlike the first games plot which centered around one pivotal moment, this games story is much more subtle and, for me, much more emotional.
The combat and gameplay in this game is almost identical to the first KOTOR. Its essentially turn based combat, though it does a good job of trying to mask that fact. All the force powers from the first game return as well as some new ones. Outside of combat you collect light side and dark side points based on choices you make which in turn influence your relationship with your motley crew of party members you assemble.
The great tragedy of this game is that it is obviously unfinished. Its ending will leave you scratching your head, as questions raised will remain unanswered. I believe if LucasArts had not been tyrants towards Obsidian this game would be remembered just as fondly as its successor. The glimpses we do get show true creativity and daring that has never been shown with the Star Wars license before or since.