When they killed off Desmond in the last game, I really wondered who would take up the Assassin mantle. I didn't understand how the story would continue without him. Add that to my opinion that AC3 was just generally a disappointment, and I'm having a hard time giving a shit about this new game. I'm not going to buy it for a while, probably (I think my roommate may have pre-ordered it, so I'll just borrow it from him if that's the case).
I really loved the Ezio trilogy. I loved getting to know his character, as well as Desmond's, over the course of those three games. Now that both of them are gone, I don't even know if I want to keep playing. Connor was the most boring main character ever, and the American Revolution story just wasn't all that interesting.
I agree with you about the setting. I LOVED roaming around ancient Europe. A few friends of mine visited Rome this summer, and they posted a bunch of picture on Facebook. Looking at all of their photos, I immediately got the urge to start assassinating Templars!