Easy: Indigo Prophecy/Fahrenheit. Like said above, it was going good right up untill it added a new (cheesy) villain for no apparent reason and completely screwed over the storyline which up untill then had been this cool mysterious ancient occult story that certainly had my interest.
And in responce to the entire Kotor 1 vs 2 thing... honestly, I prefer the protagonist from the second game more than Revan from the first. I'm sick of playing the amnesiac chosen one and essentially that's all Revan boils down to. The entire game was a one trick pony leading up to the one grand revelation. Honestly it was great the first time through and extremely well done, but other than that the story was a general redeemed villain story with a couple interesting characters thrown into the mix.
Meanwhile I liked the way the Kotor 2 non-amnesiac protagonist was presented to the player; rather than simply giving you a long monologue at the start of the game the player is learning just as much about the main character as the rest of the group, only revealing little bits at first but later on if you become close enough with some of the characters revealing large bits of the characters past that bring them to life. The Exile wasn't some grand chosen one who's fate it was to save/destroy the galaxy, she was one of Revans generals who when she'd realized what was happening chose to return to the jedi and face the consequences of her actions rather than turn sith like the rest of Revans generals did. Then, wrongfully, the council shot the messenger and used the Exile as a scapegoat, directing their impotent anger towards Revans betrayal at the Exile instead. You're simply a character who made a bad call and was in the wrong place at the wrong time, and I much prefer that over the 'you are the chosen one!' plot.
Don't get me wrong. I love Kotor 1 alot, it was and still is a fantastic game. Kotor 2 is clearly not half as good really, but it's not really the plots fault. If you take the time to actually read the full story and gain the trust of your companions, it's truthfully a pretty damn good story while it lasts... and that's the problem; Kotor 2 is only half as good a game as Kotor 1 simply because Kotor 2 is only half a game. There's no ending, none, and entire planets were cut from the game because Lucasarts told Obsidian to rush the game for Christmas when they were supposed to have had more time. Pity I say, because bluntly put if it had been finished properly, I'd say Kotor 2 coulda kicked Kotor 1's scrawny sith ass all over the galaxy.
As it is the Kotor 2: Restoration Project is finally nearing completion by the looks of it, so who knows, Kotor 2 just might redeem itself yet.