Assassins Creed 3 doesn't know what it wants to do. Like an over-stimulated child, it sees something exciting, rampages off in its general direction until it becomes distracted, chases a new object and so on. Inevitably the child becomes tired and stops playing, having accomplished very little.
Maybe this is a tad harsh, but Assassins Creed 3 is characterized by long stretches of activity that have nothing to do with being an assassin. You can't help but feel the time and effort spent crafting these features would've been better spent elsewhere. There is a solid game in here somewhere. You just have to sift through mounds of produce, pelts and plumage to find it.