This game is engaging and a lot of fun. While it isn't in my top 3 favorites, it's still very good. I just started my third playthrough.
I really like Kimahri. I think they could have done more with him. At the same time, if they did too much, he wouldn't be Kimahri anymore. It's hard to strike a balance there. I liked Yuna. She was a sweet woman with a good heart and at the end, even though the teachings of Yevon were everything she knew and grew up with, she was still able to cast that aside to do something better.
The battles are fun, although I prefer the ATB system. Talking in battle was neat. I think X-2 did a great job of that. The way you could summon the aeons and have them fight for a while was great. The turn system did allow for easy planning since the turn order was displayed right on the side. Something I really liked was how all characters participating in battle got points, and you could swap out in a fight. So I would have a few cast status buffs before finishing a fight so that they all got points.
If we're including X-2, I think the job system was great. I love job systems, or fully customizable systems (like XII) where I can make my own job systems. It allowed for customization as well so I was very happy. The battle system in X-2 was excellent and I would be more than happy if all of the Final Fantasy battles were like that.
I liked the religious overtones to X. I am religious, but I can still make my own decisions and have morals and values that are based on me as a person, and not just based on what my religion tells me to do. I have however encountered many people who can't think past their own nose and use the Bible as a character guide. Some people can be ignorant based on their faith and some can take it to the extreme and use it to discriminate against others or hurt them and I think that's just wrong. I think this game demonstrated that well. You have people like Yuna who uses Yevon to try and do good (stop Sin to bring the Calm). And then people who discriminate against the Al Bhed.
The music was very good in most cases, the towns were well done. I loved the Mi'Hen Highroad. Macalania was beautiful. Mt-Gagazet was beautiful as well.