It depends on what you want from a game. As the graphics (at least today) isn't impressive, you need something else to make the game interesting. As FF-I doesn't have a good story either, the challenge and strategy required for leveling up is what makes it interesting, I can agree with that.

To take another example: FF-X is a fairly easy game, and the second time I played through it, all the bosses were a breeze. So what makes the game interesting to me isn't the challenge of the bosses, but the graphics, battle system and the (to me) very interesting storyline. Of course, FF-X graphic will also grow old, and then it's up to the battle system and storyline to make it interesting.