I've no trouble telling you ACIII was not a very fun game, and a disappointment. It didn't kill my affection for the franchise, but between it and Revelations, damage was certainly done.
I'm tryin' real hard not to feel real enthusiasm for Black Flag, but it's getting... harder. This looks like all kinds of awesome. I'll do my best to keep in mind that despite its beauty, its fun factor is yet to be determined.