Really? The only one that bothers me is the stealth is utter bullshit and makes me rage. But sweet god the stealth was bad in all of them.
Do you mean like the economy and city scapes?
For me, Connor is my favorite assassins; best costume design, animation sets, voice actor, story. The combat is my favorite in the series; the amount of counters you can do, running assassinations, bow and arrow. The graphics have been the most enjoyable; insane amount of character activities on screen at once, the frontier makes me wet like a pony and the character models are fan-fuckintastic. The assassins story is my favorite; I actually follow it, understand the events of the time and love the characters (for a game villian Charles Lee is pretty well done). The desmond scenarios were actually interesting; minus the ending clafuffle, but I actually didn't mind it. The assassins guild was more enjoyable; being able to access the map anytime, the different assassin abilities you can use, each assassin having a personality.
But it's not ALL happy kisses and fun. I detested the stealth, felt the hunting is fairly shallow, some of the story sequences were odd, the optional objectives are made by satan, not being able to use assassins in the frontier and the bugs are a goddam disaster.
Let me say my favorite AC games to give it context: AC3 > AC2 > AC1 > ACB > Turkey Assassins > Facebook Assassins Creed Game > Revelations