Personally, I feel slightly conflicted about the third game in three years. See, I dislike Activision for running well made franchises into the ground, or letting good games die because they are not franchise-able, a la Brutal Legend. ANd now, Ubisoft is doing the same thing here.
But, two things are keeping me from hating this practice:
1) Assassin's Creed has taken steps to improve its self with every iteration, and it values all parts of a game. Call of Duty is still running off of it's same engine since Modern Warfare, and only creates what amount to mere distractions from its (admittedly well crafted) multilayer.
2) Ubisoft uses it's money to fund other unique games and experiences, and even it's own popular library is more than just the standard FPS craze. Not to say CoD has it's place, but Activision seems content with resting on it's laurels, refusing to innovate and push our loved medium forward.