Love: The concept of Assassin's Creed, the story of Ezio Auditore in Assassin's Creed II, and in AC: Brotherhood.
Hate: The stupid-ass sci-fi plotline shoehorned onto the story to explain how we are watching events in the past unfold.
Let's be clear, I love playing the Assassin's Creed series. The first game was a beautiful broken mess, but it showed amazing potential. The fact that they not only lived up to the potential, but exceeded it for ACII is still astonishing. They also created one of the most charismatic characters in any video game ever. I would play Assassin's Creed All-Star tennis if it had Ezio in it. The very idea of following this character throughout his lifetime and not just over a period of a few days or even a few weeks gave the audience an emotional tether that has only strengthened with the continuation of his story in AC Brotherhood, and soon to be completed in AC Revelations.
I can play the games for hours just running across the rooftops of Italy. Then, I have to finish the game and I get ripped out of the blissful trance I spend my playtime in. The endings of all three Assassin's Creed leave a lot to be desired. Sufficed to say I end up rubbing my eyes and muttering to myself. And that can't be good can it? I think the worst sin of the franchise is loss of momentum once you reach the end. Ubisoft has crafted this engrossing storyline carrying you throughout some of the most important years in Italian history, and then they dump you into an anticlimactic poop puddle.
I don't know what it is about endings that is so hard. It seems like so many games fail to bring all of the game mechanics to play in what should be a test of everything you have learned in your experience with the game. In Assassin's Creed II, we got a fist fight with the Pope that is even sillier than it sounds. Then in Brotherhood, we got a much more thought out boss battle against Cesare Borgias, only to be sent into an extended platforming sequence that was just pointless and boring. All of this mind you, leads you to Assassin's Creed overarching mythology that makes you sit through a somewhat ridiculous story about mankind's alien progenitors. I don't care! I was having such a good time with the political intrigue. Why? Why, must I be forced to play trial and error platforming missions that do nothing but anger me and leave me with a rather weak conclusion?
Obviously, Ubisoft cannot go back and erase the past. But Revelations needs to deliver a satisfying ending for Ezio no matter what plate of steaming you-know-what they leave for us at the end to serve as the true 'ending' of the Apple of Eden storyline. Ultimately the game is no longer about Desmond. I know they have an extended sequence set up to play as Desmond running across a virtual landscape, but Ezio has taken on a life of his own, and is owed a conclusion fitting one of the great heroes in games.