Final Fantasy X2 had one of the best battle systems in RPGs. Conversely, its story wasn't great, but I would maintain that most Final Fantasy games have equally terrible writing, just with with more melodrama.
FF fans love the battle system for X-2. My controversial opinion is that it's the worst. I hate navigating the dress sphere grid in battle, it's too fast paced, there's too many enemies that can 1HKO.