X was miles better, the battle system, the length (although still too short in my opinion, it's better than x-2) the characters, the leveling system, blitzball, the cutscenes, the music (I miss the classic style battle win tune) the spirituality, the story, the fact that there were more male characters, the summons, the fact that every one began to start knowing you, the sidequests were not repetative, the things to do after plain old winning, the ending, the monsters, the weapon/armour system, the customization system, the skills, the graphics of the attacks, the bosses which actually had some revalence to what was actually going on, the dialogue, the schemes, the nature of the enemy (in x-2 there is no real ENEMY but a machine untill the very end), the outlawing of machina...
I could go on forever.
Short version: X rocks, X2 doesn't.