The original can be challenging, though if you want the real nasty version of it, you would need to play the NES version, since that's the version where half the stuff in the game doesn't work like it's suppose to, which causes one class to really be screwed (Black Mage) and some of the later boss fights get pretty nasty since it's impossible to use debuffs and buffs that don't actually work. Origins allows you to play the original version with everything actually working; or the more user-friendly Easy Mode, which ultimately means that Mages get more spells charges, prices are half what they use to be, and enemies give more Exp. for beating them. All of the post-Origins ports of this game tend to utilize this easy mode set-up with the exception of dropping spell charges in exchange for later installments MP system.

Origins is pretty faithful to how the game was suppose to work, and it can be very frustrating and challenging for people who are used to more modern entries. FFI tends to be a very grind heavy game, either for levels but more often for gear and spells. If you're using a guide, you'll be able to avoid some of the more frustrating aspects about the game, like the fact it rarely tells you what to do next. It tends to follow the trend of most FF titles, where it's more challenging in the first half of the game before you unlock some of the more abusive aspects of the game. In FFI, that would be the Class Change sidequest and finding gear that allows you to cast stuff like Heal 2 and Haste for free and over and over. So FFI kind of gets easier as you go along, which is kind of nice because the dungeons in this game are long and brutal on item management.

In terms of replay value, it actually has quite a bit. The game is relatively short compared to later installments so it's not as much of a hassle to do multiple playthroughs. You only get to have four people in your party, but there are six classes to choose from and it's possible to even make all four of your characters the same class, so replay value comes from challenging the game with multiple different party configurations. There is even a rare super enemy in the last stages of the game that can be challenged if you are lucky enough to encounter it.