If I played X for the first time today Auron, the Aeons, the music, and some of the badass bosses like
would still be good. That boss and the cutscene before it was my favorite part of the game. Pretty much everything from Calm Lands to that scene was pure RPG adventure with a real sense of urgency and fading hope in addition to more gameplay variety and challenge, assuming you didn't overlevel or are doing some weird challenge run where you exploit a move or two.
And then afterwards you fight a giant floating whale with a blitzball.
edit: oh and Lulu is still good. Voodoo dolls are the most under-utilized weapon in videogames, and there's so much you can do with them especially now that ragdoll physics have been a thing in games for a decade+.