I'm not really a FF snob. I'm not going to say that a game isn't a true FF if it's not in a fantasy setting, or if it doesn't have moogles, or if the characters aren't developed to my liking, etc. They're all FFs because that's what it says on the package. What I've come to expect so far from the games within the package is:

Has a plot with at least one twist. All that I know of passed.
CRPG style. All that I know of passed.
The most important one of all-- fun to play. FVII and FFII failed. But that doesn't mean they aren't FFs, just that they suck.