This is not exclusive to Final Fantasy. Just about every long-running franchise has this kind of fanbase. Look at the way people hated on Zelda Windwaker when it came out and how everyone loves it now. The only franchise I can think of off the top of my head that doesn't get this reaction with every new game is Metal Gear Solid.
As for me, I like to see all the new changes with each new Final Fantasy. It shows progress.
agree with this, fans hate changes and sometimes I agree. If you have a awesome franchise, why suddenly change everything. a lot of sequels would probably be better of as just a stand alone game. in FF however I think it's good with changes and new ideas. it's not following up on the same story all the time so if someone don't want to play *insert ff here* they don't have to suffer for not knowing the story.
Then all the games in the FF VII franchise have completely different gameplay but I like that as well, it gives you a chance to see the world from a lot of different angels and can introduce new fans to the series (not likely). also they didn't make 3 classic ffvii and then a shooter, everything is different so it adds up