Warning: Spoilers
This is truly a love-or-hate game. I'm in the former camp. This game was a major part of my adolescence and I still love it now. The game play is a lot of fun and the graphics, while they've dated, hold up well enough. Graphics aren't everything.
But it's the story which has always captivated me. The themes of religious oppression, tradition versus progress, love, and sacrifice are all powerful. The characters make up the most memorable cast in a Final Fantasy game in my opinion. And yes, I don't think Tidus is annoying, though I see how he could be to others. I think his development from whiny, insecure boy to a confident man willing to give up his life for others is emotionally satisfying as well as devastating. The romance between Tidus and Yuna is poignant since the two help one another to develop as people.
The world of Spira is eastern-influenced and imaginative, and has inspired the world-building within my own stories. The music is haunting and lovely, especially "To Zanarkand," "Macalania Woods," and the love theme, "Suteki Da Ne." Of course, there are flaws. Blitzball is awful and the sphere grid is tedious. However, those are the only major drawbacks for me. I cannot praise this game enough.