Well I only really hate one entry in the series... but I'll add the ones that are the bottom of my list as well.

Hate

FFXIII - I'm going to agree with Vivi22, in a game with a bunch of insufferable whiny cliches, it was nice to have a genuine character whose problems were the circumstances in his life, as opposed to having to learn that a good part of his problems is that he is an idiot or asshole like the rest of the cast have to endure. So yeah, Sahz is pretty much the only good thing about FFXIII.

Dislike

FFX - CTB, is a great idea for a combat system that is simply just made obsolete by the mishandling of the rest of the gameplay experience. I'm happy some other games came along and did it justice *cough* Persona 3 *cough*

Not my Top Faves

FFII - It certainly has it's problems, but I don't agree the leveling system is one of them. Could it have been handled better? Yes but it's absolutely brilliant in how it works out when you incorporate it's balancing system and equipment. The system was really designed to push the player into building makeshift jobs by making them choose to optimize weapons or certain skills and stats, whose inherit balancing mechanisms would make you choose certain choices for making the character a certain way. The level of control it gave you in developing your characters was years ahead of it's time.

FFVII - I love the world design. The concept of the Lifestream and Jenova add both a nice quasi-religious mysticism to the world and the other gives it a nice heavy sci-fi angle like Aliens or The Thing which I can appreciate it. The WWII industrial design gave it a nice aesthetic touch even if I never felt the character designs themselves did it justice.

FFVIII - Squall and the concept of Garden and SeeD before the Witches showed up. I really liked Squall, and I found his growth to be one of the better ones in the series franchise. I really liked the concept of child soldiers being raised as mercenaries as well, I was just disappointed that they approached the idea in an unrealistic high school anime shojo manga style as opposed to something more realistic to the heavy subject matter the entire concept suggests. I also love the concept of the Junction system and drawing magic, it really changed how I approached battles and learning skills.