This is a good point.
From a gameplay perspective, there's a noticable drop in challenge and quality when going from 5 and 6. The Magicite system, despite being more flexible than the job system on paper, is actually less in practice and requiring them to get stat upgrades besides more HP and MP is stupid.
The game is noticably easier than FF5. Most of the dungeons are quick little jaunts that seem to end a little bit after they start and have little challenge unless you're very, very unprepared. The only dungeon that's comparable to tough FF5 dungeons like Exdeath's Castle or Pyramid of Moore is the Floating Continent, and the challenge goes back to being easy after beating the FC.
The lack of difficulty is most noticable in the bosses. The only actual challenges throughout the entire game are Air Force, Atma Weapon, and Magicmaster, and the latter is only because of his final Ultima. There's nothing like Liquid Flame, ArcheoAvis, Atomos, Melusine, TwinTania, or World 2 Exdeath, which can smack you silly if you're not on top of your game.That's not to mention that there are far fewer strategies to deal with bosses than in FFV; you're not going to be doing something like the Dark Spark + Level 5 Death trick against Atomos on FFVI's bosses.
That's not to say that FFVI is a piece of shit; it's still a great game and people should be willing to try it. It just lacks the gameplay substance and difficulty of V, so if you're more of a gameplay kinda guy, it's not going to hook you as much as FFV did or will.