On the top...
I think with game story lines, we're talking about stuff that keeps the user glued in to the action, all the while making him feel that he is in someway responsible for the way game turns out. In this respect, although full of crappy gameplay, DeusEX had a storyline that could go either way depending on the action the user took. For sheer immersement, "Warcraft III: Rein Of Chaos" takes the cake. How all the different races come together to save earth, or eventually fail to do so, is definitely great. With game sequels popping up everyday, Half Life & Gordon's fight for survival is the winner. How Valve have kept the climax for the third edition of the franchise is totally enthralling.