I guess you feel this way because the main character is different. The entire series excluding the first Assassin's Creed you play as Ezio and he's been the main character ever since. I've played and beat all of the games in the series and I'm looking forward to AC3. If you liked all of the other ones, I suggest getting it and if you aren't sure, rent it.
I cannot recommend and of the AC games enough!! Revelations was a little meh... but still a good game. Of couse I am super stoked about AC3, just make sure you have played the other first, some serious backstory