Video games are like movies. & the vast majority of movie sequels suck because they are cheap imitations made only to cash in on the popularity of the original. I love a good concept just as much as the next guy, but if a game company is going to put all the time & effort into a sequel, give me something new, else I won't bother to waste my money on something I've seen & done before, just with a few new extra bells & whistles.
I have to say diversity in sequels is what has kept me buying FF games. Whilst the core ideas remained unchanged until XII the way in which characters developed has never remained the same since VII. From little stones, to junctioning using your summons, the abilities and levelling system has always added something to the basic concpet of run, fight until you get to the next cutscene.
It's also what's kept me coming back to the Total War series.
Sequels should keep the core of the original intact, and all those you mentioned do pretty much exactly that, what's different is in the way they do the other things. That diversity is key to keeping a franchise fresh and exciting. Rather than simply being EA's perennial sequels of their core titles. Which let's face it are the same games year after year. Just with newer rosters.
I, for one, would hate to go back to the Genesis/SNES era when a sequel was simply the first game all over again with a different plot.
Saint Del is considered a holy healer of diseases of children, but also as a protector of cattle.