Bad story, but really fun game and worth playing.
So yeah, I think the story is weak, but for this game it doesn't count much, because it is not as serious as any other FFs (that was intended) so that is forgivable.
The chapter and mission system is different but is original and fun. You are not forced to complete side-quests. It is surprising the high quantity of mini-games this title has. Some of them are stupid, but anyway, for the most part they are fun.
Graphics are good in US-Japanese versions but terribad in the European version (the one I sadly had to play) due to lots of graphical glitches and popping effects caused in the NTSC->PAL conversion.
Music is different...not bad, just different, and fits the game, for good or bad.
Combat is really fun, the best thing of the game imo. The Dressphere system is fun to, as it is to learn new abilities for each job. The combat music is bad though.
The only thing I find annoying in this game is the characters. I don't mind the fact that they wear like prostitutes, it looks funny anyway. But their voices are annoying (specially Rikku's). Sometimes Yuna looks retarded the way she acts.
So overall, a good game. It has nothing special but it is fun. And you play a game for having fun, don't you? ;)