Basically what ^^^^^^ said.
The battle system is both ludicrously complicated and very simple at the same time. It is also hilariously fun. It's pure action, and I often find myself fighting enemies just for the hell of it instead of advancing the plot.
The food/item/clothing system is a little bit overdone, in that I think they put too much equipment in, for example, you can go into a store and there will be 5 or 10 shirts that aren't all that different in ability or power. It's also a little unclear on who can wear what and the game doesn't tell you other than how much "Bravery" they require (ie if I get Neku's Bravery high enough, will he be able to equip the Plaid Miniskirt??).
The story is very well done, it's more of a dark/modern game like Persona or Shin Megami than a typical RPG, and the characters are quite endearing (now that I'm on week 2, I really miss Shiki).
I'm afraid it'll get overshadowed by FFTA2 (which I just picked up and haven't tried yet) but hopefully it'll sell enough for a sequel, because there's so much that could be done with the basic concept.