I'll put in a kind word on FFVII:
Is it overrated? Yes, most definitely. But is its popularity well-deserved? Absolutely.
Like most popular side characters that become main characters in a show or work of literature, over exposure is slowing doing in FF7, which has since spawned its own OVA(have yet to see it), movie(loved it), and three spin off games, only one of which was available on a platform console, and therefore, capable of the same quality overall as the original. Now, this has had some degree of success, as well as some degree of failure. I freaking loved Advent Children, and even if I accept it as non-canon, it was worth the price of admission/dvd/pirating it off of the Internet/what have you. However, at a certain point, enough is enough. The original game was amazing; rivaling FF6 and 9 as the best Final Fantasy game. I have a feeling that even the most ardent fans would agree that a third game in an RPG series that everyone here had better be aware of, would've been better than a third spinoff of FF7.
Now where's the kind word in all of this? Well, FF7 definitely deserves this popularity. Consider Pop Rock, an entity far more mainstream pop culture than Final Fantasy games will ever be(outside of Japan, anyways). Where are Hanson, most of the members of N-Sync or the Backstreet Boyz, who just ten years ago, you couldn't walk into a public domain without hearing something good or bad about one or the other. Now consider them today, where very few of these people still exist in the public eye. They're popularity was ill-deserved and fleeting. Now consider bands like ACDC or Jimi Hendrix(yes, he was a band in and of himself). ACDC is still doing tours around the world, and I'm sure Hendrix would be had he not died of a heroine overdose. Moreover, fans of both still wait for ACDC to do a tour, or come out with a new CD, or for another Hendrix cover band to pop up. I'd consider these people's fame much more deserved than their pop rock successors.
What does this have to do with FF7? Well, 15 years after it was released, there is still a clamoring for a new spin off, or new OST release, or cameos, etc. That there is such a demand for this franchise so long after the original debuted shows that there is a bit more to it than the shallow popularity of a fad. FF7 had something that touched and inspired people, so that even 15 years later, people are still wanting more of it; to interact with its character again, or fight the same story again. It was the first on the PS1, and hosted an extremely cutting edge graphics engine for its time. It's spiritual successor in this regard, FF10, had no such love from its fans.
In short, FF7 is a standout game and franchise. It's overrated, sure, but at least its overratedness is made less sufferable by the fact that it deserves the popularity it has.