Balanced Design, as I've mentioned before in other threads on this type of topic, FFs strong point tends to be being better balanced in all aspects of it's functions than other games or series. The series may not have consistently great story/characters/gameplay but they are generally consistent (until the merger at least) to have a well packaged deal with minor gripes and complaints. Usually if one thing is bad, then there is almost always two or three things that pull it out of being terrible because they are so good.

Other RPG series tend to always lack something for me, or at most, can be balanced enough to not be offensive in any way, but sadly also balanced enough to not really have anything stand out either.