People are saying it'll be too focused on the naval warfare, but mostly that it won't feel like an Assassin's Creed game, etc. etc. everything they've been saying ever since ACII and been proven wrong repeatedly.
Even people complaining about how soon it was announced. ACII, Brotherhood, and Revelations came out within a year of each other IIRC, and they were all great games on their own merits. I trust Ubi on this.
EDIT: I'm calling it now. East India Trading Co. is Templar, and that's why the Assassins had to resort to piracy.