Opposite of FFXIII: FFXII. Greatest RPG in 10 years? Psshhh.
The sad thing is, no matter what they do with FFXV, at least half of the Final Fantasy fans out there will probably call it horrible purely because there are so many of us these days and they all have different ideals about what would make the greatest FF ever. The first fourteen games are so varied in their nature that fans of each individual game are as different in their hopes/expectations as the individual games are different to each other.