Let me ask you this: What makes a Final Fantasy game?
Long running games have common themes among them. Recognizable enemies, locations, characters, worlds. If you played a game and liked it, chances are you want to see most of what you enjoyed on the first game on the next one.
Final Fantasy, however, decide to scrap everything and start anew every time, giving me little reason to follow the series. Worst, if I actually enjoyed any given game, chances are I will hate the next one because it will be anything BUT similar to the previous.
XIII, good or bad, barely remind me of a Final Fantasy game. They could call it "Destiny Crusade" and I would not know better... except by a hint, put there to alert me: there are Chocobos.
The yellow bird is the last straw connecting the series for me, and the mark which Final Fantasy separate it from it's lowly chocobo-less RPG brethrens.