I though FFX2 was a necessity. The ending from FFX was too open ended, and the world was in a state of ruin
i disagree with that, a lot of the endings to FF games have left ruined worlds, eg IX after brahne, then kuja tries to destroy everything. imo, X-2 wasnt neccessary, but square-enix kind of implied a sequal after the final credits for X so it was knd of inevitable anyway.

As for what it lacks, a decent story. X-2 has a story that makes you want to shoot yourself with yuna's guns. It's awful compared to X and the other FF's. the musics ok, but i wish they used the prelude theme and a proper victory fanfare arrangement found in almost all FF's. It lacked a decent overdrive system, which is what i consider the special dress spheres to be a poor attempt at, and of course, it lacked decent main characters, lacking the strong knowlegable type, ie Auron, that people here think Paine was supposed to be