Quote Originally Posted by aisle_s
FF1: Groundwork
FF2: Adding complexity (slight) to the storyline
FF3: Innovation to the battle system (jobs)
FF4: Deeper characters and story
FF5: Nothing too special, a job system remake and mediocre story
FF6: Deepest of characters and story so far, new innovations to battle
FF7: Very good story line, little innovation
FF8: Very good story, many well developed (and some under developed) characters, lots of gameplay innovation
FF9: Very good story, deep characters, some battle innovation
FF10: Original story that wasn't handled well. Very good, fluent, and innovative gameplay (sphere board/CTB)
FF11: Experimental, in my opinion
FF12: ? Who knows.
I agree with most of what aisle_s has said, and I do agree somewhat with the earlier presented categories as well. I like aisle's list because it's game-specific. Some modifications I would make:

FF5 is a much more fluid version of FF3. Jobs and Abilities and everything just makes more sense now. While the story isn't much to behold, in relation to its predecessors it's quite good, about on par with FF4.

I think the FF7-10 have had the most innovation so far. The expanded processing capabilities of PSX and PS2 allow more than just a standard menu. I also agree with the emphasis on romance in the story line and a paradigm shift in game making from "playable video game" to "interactive movie". This corresponds with less detail on storyline and more detail on character development. This also corresponds with the lack of gameplay innovation that is overcompensated by obscure (albeit interesting) ability system innovations.

I was actually relieved to see the return of the updated CTB in FF10, and enjoyed being able to manipulate the lineup. I think FF10 was just as experimental as FF11, and it didn't perform well in some respects, but I am a huge fan of experimenting, and overall FF10 really impressed me. As opposed to FF8, which also had a ton of innovations, but the lack of a driving story.