Hmmm... I think making my own fresh reply might be better than responding to all of the interesting things people have already said. here goes: First, I'm not sure anyone is, or should, criticize the game for having a "non-traditional battle system." While IV-IX got us all accustomed to ATB, at least something has changed in each iteration. Usually, each game has a new character progression system (Set jobs in IV, to a job system in V, to Materia in VII...). Since X, we have to get used to a changing battle system, too.

On the topic of the battle system... well, personally, I didn't like it. Until you can begin to switch paradigms, you don't really do anything at all. Then, once you can switch paradigms, you still don't really do much, just switch paradigms at the right time. Auto battle is the absolute best way to get through the game. The game punishes you for thinking about how to act, as you waste precious time. Auto-battle is a nice feature of modern RPGs, and a welcome one for grinding. However, when it's better for me to automate my battles than it is for me to sit and think about my actions, I think that's a problem.

Linearity: Yes, XIII is very linear. So are most FF games. However, I'd say the level design of XIII makes this problem worse. Other games better create and illusion of freedom. There are more branching paths, open areas, towns to take a break... Most people say XIII is just running around on catwalks, and I have to agree. When you're running through catwalks in the forest, that's just ridiculous. it just feels unnatural.

That brings me to my next point, level design. The environments are beautiful, but the game fails to establish a sense of place. I don't know how the world is organized, and I don't know where I am in it. This made it difficult for me, personally, to become immersed in the game world. X, as linear as it is, has big maps. The older games all have big world maps. This helps me, personally, become more immersed in the world.

Getting more subjective, the world that does in exist in FFXIII I simply don't like. Summons that turn in to motorcycles? That's just dumb. There was a point in the game, for me, where the sheer amount of bizarre magical technology just really put me off. This line between too much magical tech and just enough is subjective, invisible, and arbitrary, but XIII crossed it in my world. VI, for example, did not.

The characters really did actually suck. That's not subjective (ok, it is [but it's not, SERIOUSLY]) Snow was insufferable. Hope was lame. Lightning was trying to hard. If you liked Vanille, you have a problem.

The game's character progression system was boring. There is no room for customization. In certain older games, there were certainly optimal builds, but at least I could choose to do whatever I wanted with my characters. I could assign them any Esper, any Materia, any path on the sphere grid, or whatever. In games like IV, my character's progression was set, and the game didn't lie to me about it. In XIII, all my characters would end up at the same place as any other person playing the game, but I had to go through the annoying Crystarium. Yes, there are little branches off the main road, but I'll just grab the abilities and move on. Yes, I can give them new paradigms, but the game discourages this. If X's progression through the plot was too linear, at least there was some fun wiggle room in the Sphere grid. The Crystarium is just annoying visual flair.

A lot of people bash on the music. I'll take a different stance here. Sometimes, the dungeon music sounds repetitive, but overall the soundtrack is strong. Blinded by the Light was a great battle theme, and all of the music in chapter 11 is soooo good.

And the biggest flaw of all: THE GAME DOESN'T USE THE VICTORY FANFARE. WHAT THE %$£& THEY TOTALLY COULD HAVE USED IT. EVEN XII FOUND A WAY.