Simply amazing..
It's.. It's just great. Everything is good; the battle-system, the graphics, the story.. It's pretty easy to learn, but the game isn't that easy, so casual players may have some troubles with the game. I loved boss fights, the monsters looked amazing..!
Your characters are also nice:
Tidus, the young fighter / blitzball player; Wakka, the ranged fighter; Lulu, the black magician; Rikku, the Al Bhed 'mechanist'; Kimahri, a fighter of the Ronso tribe; Auron, the 'strong guy'; and finally, Yuna, the Summoner.
The main characters are Tidus and Yuna. Yuna can summon Aeons, (strong summoned creatures) so she is very useful. [And don't forget that she can heal/revive!]
There are some good mini-games and puzzles too, so it doesn't get boring. You can spend around 100 hour on this game, but if you want to get every ultimate weapon or armor, and defeat every single Dark Aeon you need 200-300 hours.. Everybody MUST try this game! :)