I finished the Steam port of SquareEnix's Final Fantasy III. It took me a year, and having to go all the way back to the start to relearn the job system, but I did it.
Final Fantasy III is a role player's RPG. The job system makes the characters much more customize-able than other early titles in the series and the lack of save points in dungeons make proper supply and strategy non-negotiable. All-in-all, it's the most difficult classic role playing game that I've encountered -no wonder it took so long to hit the U.S. market.
That said, however, what would have been a disadvantage when I was a kid is now a major selling point of the game. Final Fantasy III requires and rewards thought and care as players delve into its lushly imagined world -and a delightful world it is! The tone is light and upbeat with its Funkopop-like animation and sense of high adventure, but without the kiddieness of a Secret of Mana (though it also should be noted that there are no moments to compare with Aerith's death or Celes' opera). The world of Final Fantasy III also coheres in a way that the world of Final Fantasy VII doesn't. It's high fantasy all the way and no superfluous towns or elements that seem like they belong in another game.
The final word on Final Fantasy III is that it's fun. If it doesn't soar as high as later entries in the series, it also avoids their pitfalls and provides a more challenging play experience.