-The game is too easy
-The story sucks (no offence to those who loves it)
-The Sphere grid system sucks
-Magic sucks (even with hight magic stats)
-Evasion/Accuracy stats are unballanced (You could hit everything that had 50 evasion with 50 accuracy, but always miss when attacking something that has 255 evasion with your 255 accuracy character)
-You're going to press your analog stick ''up'' A LOT (Seriously, I don't thing I ever went in another direction than north in the whole game)
-Way too linear. Appart from a few exeption, world map-less games sucks.

FFX is a good game, a mediocre RPG and a very crappy FF (probably the crappiest IMO)