bugged features in the original fixed in the re-release, I'm playing the game I only thought I was playing as a kid.
Overall (bugs included), the original Final Fantasy had a huge problem with class balance. The fighter was hands down the best class dealing the most damage and taking the least. The black belt was good but not great; its saving grace was that it required no armor weapons or spells making it a cheap class. The thief brought nothing to the table except running. The red mage starts strong but fizzles out mid game. White and black mages were practically essential for their magic, but didn't have enough spell points to keep them running, so they mostly sit out during combat. Fixing these issues required some changes to game mechanics.
The biggest improvement made is the revamped magic system. The original had eight spell levels with four white and four black spells at each level. A character can learn three spells at each level and, as a character leveled up, it would received an increasing number of casts at each level. The modern edition kept the spell management the same but changed the casting cost to the now standard mana points system. What a wonderful change this is. Now that the spells are much less scarce of a resource, the player can use them freely instead of having to save them for an emergency which might not even come.
I remember playing FF1 for the first time and never using any of the white level five spells except for life. I could have used them, but because life was such a critical spell due to some monsters having instant kills, using them meant I might not be able to resurrect my characters when I needed it. The additional flexibility gained from all spells casting from the same pool of points means that cure can be cast more than nine times per rest. Putting a rubber band on a turbo controller to automatically buy 99 potions is no longer required.
The mana points change is also a major boost to the over-all power level of the black mage. In the original it was mainly left on the sidelines waiting for a tough encounter at which point it would explode on the enemies, winning the battle in a single round. Now there are trade-offs. The mage still has to budget its resources, but doesn't need to be a total scrooge and can afford to cast a spell every round.
The second biggest improvement is the addition of new items. In the original you were practically required to bring along a white mage to take care of various ailments. Now there's an item for every situation that may arise. Instead of bringing along a white mage that mostly takes up space in combat, now you can bring along another damage dealer. While that may not be the best decision, it's still a viable option, which makes party choice all the more interesting.
The art and sound in this release is pretty much a wash. The art was updated to a 16-bit look, but not re-imaged from the original Amano sketches. The music was updated to a fuller sound, but without the love. The overworld theme and battle music were much improved. The temple of fiends was just okay. The earth cave was terrible. They started the song in the middle and made it kind of twinkley. Why would anyone make the music in a cave of rotting earth happy sounding. They should have just taken the music from Final Fantasy Symphonic Suite it really doesn't get any better than that.
Overall, it's a joy to play through it again. I'm glad its design has held up so well. Even though it's easier, it still keeps you on your toes. Even when you know what to expect, bad luck can leave you in a tight spot. It's challenging, but not unreasonable. There's much more to it than I remember, yet still remains a simple classic RPG.