Some of my thoughts after playing through FFXIII that I couldn't really fit in short forum reply. I tried to stay away from gameplay elements like the battle system and character development, which although I have opinions on them are kind of subjective love-it-or-hate-it elements. I wanted to instead focus on what I felt were certain deficiencies of the story telling and why it dragged down what I felt could have been a great game into the wide realm of "just O.K." There are several things that go into making a good story, to whit:
The Story Needs to Be Well-Told: This is kind of a duh, since a well-told story is what keeps people playing, but one of the most important aspects is pacing. A good story has a certain rhythm to it. There is frenetic action followed by a short period of recovery followed by more action. Too little action and the story loses momentum and gets boring. Too much action and you just go numb. For a good example of how pacing is imporant, look at a couple of movies - Raiders of the Lost Ark and Transformers. Raiders is an example of a well-paced plot. You have the inital thrill of the escape from the temple, with the boulder and the escape from hostile natives, but the audience is given a rest when the setting shifts to Indiana Jones teaching a university class before ramping up again with the bar fight. In this way, the plot keeps moving along at a good clip while not inuring the audience to the fights and explosions. The "rest" portions of the movie help to make the action sequences even more thrilling.
Transformers on the other hand, is an example of poor pacing (and why Michael Bay should not be allowed to direct movies, particualry ones involving franchises from my childhood. He's going to ruin Thundercats next, just you watch). Once things start blowing up, they keep blowing up. Thrilling at first, yes, but after 2 hours of it non-stop, the audience is just sort of numb. More explosions don't really register because you have nothing to compare it to other than the last explosion.
FFXIII has O.K. pacing, but it is too uneven to be really excellent. Partly this is due to the interaction between the gameplay and the cinematics. There is rarely a point, particularly in the early going, where you have large stretches of either one. You typically fight a few battles and then watch a short cutscene followed by one or two more battles and another cutscene. This has a tendency to make the action feel really chopped up and disrupts the flow of the plot. To make matters worse, you are constantly shifting from one party to another. Just as one gets interesting and you get invested with what is going to happen, you are wrenched away to a decidely less interesting and intense moment with another set of characters. Although cliffhangers are a good way to build tension, too many makes them lose their effect.
This is where the decision to omit towns kind of hurt FFXIII in my opinion. Towns give you an opprotunity to sit back and absorb any releveant plot points you have just experienced, as well as being able to get a "man-on-the-street" opinion from talking to NPCs. There is certainly a valid arguement that towns are not needed and only serve to slow down the momentum of the plot, but getting rid of them means all the exposition has to come in the short bursts present in the game, which chops up the action.
The World Needs to Be Fully Realized: This is probably one of the single most imporant aspects of an RPG - the world the characters inhabit needs to feel "lived in". This is how a good RPG gets players to buy into the plot and suspend disbelief. This is particularly important because RPGs tend to have such out there plots. Games like the Mass Effect series do a really good job of this. For a more FF example, look at VII. On the face of it, the basic set up is kind of absurd. One mega-corporation (and an energy company to boot)controls most of the planet, which consists of one gigantic city and a bunch of rustic villages. The thing is, once you buy into it, it does not seem that strange. The beginning segment of the game in Midgar does a good job of setting up Shinra as a monolithic opponent and so its omnipresent control of society doesn't seem so far-fetched. In this way, games get you to ignore things like one of your characters using a sword while another has a machine-gun arm.
FFXIII I felt really struggled with this aspect. I constantly found myself looking at all the inconsistencies the game world presented, but was not given any plausible explination for them. For instance,
Although some of these questions were eventually answered, it was not done soon enough to get me to buy into the world the game had created and by the time these details were revealed, it felt like some lazy deus-ex plot point rather than a believable part of the world.
There Need to Be Things to Do: No matter what RPG you play and no matter how well designed and constructed the plot, eventually most players will get bored grinding through monsters and want something else to do. A good RPG provides this for them, typically by one of two methods (or both) - sidequests or mini-games. Sidequests are typically non-main story essential plot threads that either give you insight into your characters, more fully develop the world the game is set in, or both. A good example of a well-constructed side-quest chain is Vincent's story in FFVII. As an optional character, Vincent would be easy to ignore, but by performig his side-quests and discovering his relationship to Lucrecia (and by extension Sephiroth), you get insight into his reasons for coming along. He no longer feels like a "secret" character and feels more like an organic part of the party with his own reasons for coming along on the journey.
Mini-games are more along the lines of traditional "filler" in a game, but can provide a welcome break from the main plot. They are also usually incentivized by letting players win powerful items if they invest enough time into it. A good mini-game doesn't take a long time to play and offers a different play experience for the gamer. Triple Triad from FFVIII was an example of a near perfect mini-game. Each round took maybe 60 seconds to play, but it also had a good level of strategic depth. A player could easily spend a good chunk of time doing nothing but playing Triple Triad, and would come away feeling reenergized to take on the main plot.
FFXIII is a bit odd in that it really doesn't have either mini-games or sidequests to speak of. As a result, it can be difficult play in long stretches, especially if you hit a frustratingly hard or boring stretch of gameplay. This hurts it not only in the fact that you have nothing else to do if you get frustrated or bored (which can be easy with the on-rails level design), but there is also nothing to really flesh out the world the characters inhabit. The game has a ton of wodnerfully designed environments, but there isn't really anything the player can do to explore them. There are not any "secrets" in the sense that you can explore an area and gain greater insight into the world than most of the characters would normally have.