This game gets a lot of buzz, and not without reason. I've played the original SNES version - I still have the original cartridge I bought at a Gamestop when I was a teenager - and the updated GBA version. This game was also updated/released to several other platforms including the Playstation and PC, but I will stick to the NES and GBA version as these are the ones I have experience with.
Unlike the last three games in this series, this one does not talk about elemental crystals, and has a much deeper story. Not that the previous games weren't enjoyable, but a new story certainly was refreshing, and we also got more depth to pretty much all the characters, including some quite tragic backstories. This also has the largest cast of characters, for a total of 14 if I recall correctly, though ultimately, four are optional (if you make the wrong choice, you lose one permanently, two can only be discovered with secret quests, and the fourth one is with you for the first part of the game, and you can choose to get him back later in the second part if you're so inclined)
This versatility and skill sets in the characters offer you a lot of options for your party. All your characters, except for one, can learn magic from Espers regardless of their skills, though their magical strength will naturally vary.
This game offers a real mindfuck at several points story-wise, and several choices will have real impact on the story later on. You will have character deaths, mental illness/insanity, exploitation of sentient creatures, and slavery, so this game may not be for those who are really sensitive, but I feel that for its time, these topics are handled appropriately.
The graphics and gameplay are pretty great. This holds true for the original version, and is polished for the GBA, along with the addition of several bonus dungeons/quests in the remake. If you like RPGs, this is definitely a game to try.
Grade
FF6 (SNES version) A-
FF6 (GBA remake) A