This. Ezio is cool and all (as is Altier) but it would be nice if we moved past them into a new character to, you know, advance the story. Brotherhood was fine with Ezio because they needed to know where the apple was in modern times, great, fine. Ezio has served his purpose, we saw him rebuild the Assassin's order, get the Apple back (again...) and hide it. Altier could have more to show but we learn a lot about what he's been up to in AC2 with the pages don't we?
It'd be nice to have a new character, because one of the great things about the AC series is that a game could have you control anyone from any time period, and even (if they go for it) explore Edan with Adam in the time of the ancient people.
I'm hoping that the next game is AC3 and has you playing as Desmond, doing modern day missions and as Adam in Eden finding Eve or whatever he needs to do.