My image of what makes a Final Fantasy game has become more vague over the years. A simple description might be 'Stories of a small group of people saving the world from a big bad with some pretty crazy plot elements in them that are quite a lot of fun to go through with awesome music playing all the while'. But also, Final Fantasy in particular has always has its recognizable elements in its story, gameplay and characters. Like how you can find themes of nature vs technology in pretty much every instalment.

I can at least say that I don't think any of the recent instalments have 'betrayed' what Final Fantasy really is / used to be.