Yeah it is the last great FF game. Series has been on a steep decline since then. Not surprised OP liked 12 (which sucked)
I have my reasons for not liking 10.
I didn't like that they took away letting all your characters have summons.
I didn't like the leveling system.
I didn't like the designs of tidus, rikku,lulu, Seymour, or really even most of them if I'm being honest. Tidus has one of the worst fits in series history.
The dialogue was very awkwardly written. Maybe it was always bad, but hearing them actually have to say that shyt was embarrassing even to me as a 12 year old.
The limit breaks were unimpressive.
The game had no humor, or more accurately all the attempts at humor fell terribly flat.
12 felt like a step back in the directions that made me like the games while evolving the formula. Mist combos were fun, letting you customize your characters so they weren't restricted to one weapon was a risk that paid off. The voice acting sounded like it was done by professionals. I liked the different summons. The dungeons were more fun, and became addictive as you tried to get better and better loot by keeping your steak of W's going. The towns felt more alive. Each character felt unique and like they could each carry their own spin off game. I enjoyed playing from the point of view of the different characters to learn them more. Its not a mainstream opinion to dislike X and that's partly why I feel comfortable saying it just didn't grab me the same way as it apparently got others.