I beat Assassins Creed III about a week ago, and now I'm just going back and finishing up all the other little stuff around the game. The environments and gameplay tweaks are definitely improvements over past games, but the ridiculous amounts of bugs and glitches kinda took away from the whole experience. Some sequences were a lot more difficult than the rest of the game, particularly chase sequences, and I feel like that was more due to clunky controls more than anything else. I also felt that some things they tried streamlining (side quests and whatnot) were good in theory, but just became confusing in actual practice. The Desmond sequences were huge improvements over previous games, although the ending of the game definitely gave me mixed feelings. Definitely a good game, but I don't think it quite lived up to the others in the series. If they do a "Brotherhood" equivalent of this game, I expect it to be what this game should have been. The QC was just not as good this time around. This supposed "Thanksgiving Patch" looks to be fixing a lot of the problems, but I still feel like the game was rushed into distribution in order to compete with CoD and Halo 4.
p.s. The multiplayer is awesome, though. They definitely spent some time refining that one.