I know this is an unpopular opinion, but I thought X-2 was a fantastic game. Gameplay-wise, it slapped. The battles were fast-paced and fun and still had that classic turn-based feel (perhaps the last FF game that really did, come to think of it). The story added so much depth to the world, specifically regarding spirituality and the physicality of memories, that it made X a better game.
Honestly, I wasn't too sweet on X when I first played it. After the hits of the PSX era -- especially IX, which was just wall-to-wall awesome -- X was a letdown for me, even though it was a good game. I was expecting more from the first PS2 game. In hindsight I realize that was just my own misplaced expectations. IX was a love letter to fans like me, a perfect way to wrap up the era, and X began something new, something different.