Since I mostly went into details on Dissidia, I wanted to make a few other quick mentions that didn't really fit in... I'll try not to spoil, but it's probably mostly going to make sense to those that have played.
-Alt-version Sephiroth. Oh damn, it's nice to have some fanservice for the GIRLS for a change.
-Holy damn, Kuja doesn't only look like a woman in this, he sounds like one too. o_O (Seriously, this is coming from someone who likes her men pretty.)
-So much hate for Ultimecia's Castle. So. Much. Hate.
-This game is bringing out a usually-buried sadistic streak. Some of the best "dialogue" I've found is the anguished death screams of certain characters. Mmmm.
-The in-game help tutorials/manuals? Awesome. XD
-Dude, I don't think I'll ever come to the end of the content!