I loved the "Good Ending" scene in X-2 and the promo video about the Eternal Calm. those IMHO added to FFX in a good way

The rest of X2 was much too different and too girly and superficial. Which sets it miles apart from X which was quite dark and serious with is jab on organized religion.

I ended up forgiving X2 for spoiling X because the battle system was slick and fun and the dresspheres were very powerful. But yeah, as a sequel to X it failed.