I think that if you play through normal mode and get the feel of the game, then when you play expert mode the game will be harder because the enemies hit harder but easier at the same time because you already know what you are doing and how to best fight enemies. Although, even with that, I still died several times fighting some of the bosses before I got the cure spell, so it is quite a bit harder. Even Tidus, Selphie and Wakka are harder in expert mode.