Like others I've got to chime in and say "one of the Xbox's best exclusives". A must buy if you like Sakaguchi's older games (i.e. Final Fantasy 1-10, Chrono Trigger). It's EXACTLY like another Final Fantasy circa 6-10, which is a great thing.
I hate that it never got a sequel. It's a full story, I don't feel ripped off or anything, but there's...room...in the story that they easily could have done a direct sequel.
Blue Dragon's got good gameplay, but the story's much worse. His newest, The Last Story, was better than I'd feared, pretty good, but I didn't like the story half as much, and while functional, I vastly prefer an active time battle system type-system to The Last Story's action-rpg mechanics.