FF5 is IMO the last of the FF series that may pass as an 'intellectually challenging' RPG.
A tidbit from December 1999.

And here's a gem from June 1996:

FINAL FANTASY III'S LAST BOSSES ARE THE BIGGEST SHAM IN VIDEO GAME HISTORY
(III referring to VI.)

The fact that VI is "too easy" and "not as good as IV" comes up a LOT on this newsgroup. That last quote comes at the end of a huge rant about how FFVI is both easy and very boring.