I have played several turn based RPGs like the first three generations of Pokemon and Super Mario RPG (beaten over 100 times in the last 22 years) but never had played Final Fantasy anything. Then I played the SNES (USA) version of this game. Knowing game came out before all the ones I listed, and having played NES, for the times, the graphics are amazing. The ATB really adds a lot to this game, tho coming from Mario RPG, the closest to FF gameplay I've had, the lack of timed hits took getting used to. The character development is really awesome too, and that it was given 1991 graphics/sound makes this game all the more important in video game history. But the best part by far is the music. The melodies are beautiful and stirring, tho I will say: it sounds way better on SNES than all the enhanced ports.
I first played the USA version, and then played the Japan version with a fan translation. Play the latter; its the real game with way better dialogue, items, etc.
To truly understand the development of video games, as well as for a good game, play Final Fantasy IV (aka FF II for the US release). This is FF5 are the best in the series.