Nothing special...
There's not much to say about the storyline, except for a couple of twists here and there, but all in all, it is very predictable. It's the usual evil emperor bent on either collecting or destroying some artifacts of importance and value, and you are the unwilling hero who becomes a part of the whole shenanigan. Although on your travels, you visit different areas and meet new people, the towns have no special traits and all feel very crusty (and forgive me for saying this: old-fashioned). I was personally hoping for a new, re-vamped world map with new towns, but no such luck.
When I watched video footage of FFIV, I felt really excited because of the ATB system. Its great at first, but eventually it gets very old, very fast. You constantly receive new party members (which is another feature that I thought let it down), and each of those party members have either 4 - 7 types of basic commands. Attack, defend, row (changes position of party members) and the rest are determined with the type of character you are using. For example Cecil, as a Dark Knight, has the above commands, as well as Darkness (like in FFX-2, which attacks a group of enemies at the expense of your health). Each player has unique abilities. Other abilities include magic, jump and examine, to mention a few. The battle system, while fun at first, becomes very tedious as most of the time you barely use your special abilities, and just stick to normal physical attacks or magic attacks.
Although not visually astounding as most Square creations nowadays, Final Fantasy IV looks decent. The overworld where you travel from town to town looks EXACTLY like Final Fantasy: Dawn of Souls, so if you have played that game, you know what to expect. As I mentioned before, the towns have nothing special about them, no distinguishing traits or theme. However, there is a decent amount of land to explore, so it'll provide you with enough fun to last you hours.
The one aspect of FFIV I was impressed by was the music. Although it became repetitive, it rarely become painful to listen to. As a special reward at the end, you get to unlock the music player (which I think was the only thing that kept me going). Nobuo Uematsu really did a solid job, and it pays off. You'll just wonder around aimlessly to listen to the music, and in my opinion, it even better than most music in games today. Weapons and magic also have their own distinct noises when they are put into effect which is a treat to listen to.
I don't think I'll be playing this game again in a hurry, and I'd much rather wait for Final Fantasy XII which looks very promising. Had there been a more solid foundation for the game, such as a constant set of party members whom you can customize and less predictability, Final Fantasy IV may well have been one of my favorites games of the year...