I found Ezio's story interesting. Don't tell me that if you saw half of your family murdered you wouldn't want to exact revenge. And then uncovering a giant conspiracy in the meantime, that would be awesome.
And in all honesty the first game didn't give us a chance to really see Altair's personality, other than breaking the basic tenets of assassin's at the start, all he did was atone for them during the game. Had we seen a spinoff for Altair solely (not talking about Revelations) maybe this topic would be a little more relevant.