XIII unquestionably in my book, because I enjoyed the rest of the series so much, the only way they could've lived up to more potential is if they closed the gap between their greatness and original design. XIII on the other hand... I got chills when the trailer came out, I must've watched it a thousand times in anticipation of getting my PS3, and the music gave me chills nearly every time. All the crazy action and beautiful landscapes seemed exactly what the series was all about, then it turned out they had no game design at that point and still wouldn't until about 3 years into the project. Like the game, but it's hard to understand how one of the premier houses in gaming stuttered so badly... ok I guess it's not hard to understand, we discuss it here all the time...

This is a great thread though because I believe Uematsu said the only thing the FF games have in common is that they're all unfinished.