Final Fantasy XIII gets the fundamentals right, but fails on the execution.
Arguably, storytelling is the protagonist in each Final Fantasy iteration, where you can count on lengthy game-play to accompany it.
Unlike their predecessors and also current jRPGs, FF XIII tries to give game-play sense within the story and also by being logic instead of being a separate entity from the story.
The sense of starting at level one, while coincidentally finding only monsters of your level as the game progresses is eliminated; the excuse to enjoy the ability of using magic unlike the commoners is well founded making the protagonists genuinely special. Add to that a better, more transparent transition to battles with a genuine dynamic strategy within it; you get a consistent world that blends game-play and storytelling instead of abruptly becoming one or the other.
Narratively, improvements favoring logic are also implemented: your party doesn't stay together happily during the whole adventure as if they were part of a kids tv show. And the lore is built upon a more realistic view of society where power can dictate the truth and freedom fighters can easily be labeled as rioters and dangerous individuals.
Not to mention that graphically the game becomes even more real, plausible and palpable, with a realistic scale and proportion of scenarios, wild life, buildings and paths; while inherently shrinks the possible size of the maps, it greatly enhances the veracity of the existence of the characters.
However, the disgrace for Final Fantasy XIII comes with a series of ill-conceived design choices that, at times, completely nullify the great choices.
Linearity is essential for a cohesive plot, to purposefully cause a meaningful impact on the player. However a demonstration of a blatant lack of creativity by the level design team, makes this Final Fantasy a very, very long and dull corridor with some meaningless branches that either give you items or are just completely useless.
Battles also suffer, specially when common and irrelevant fights can last twenty minutes or more if you are not using the correct characters, therefore nullifying the special aura surrounding our characters, when you can barely damage simple guards that would crush you if they could heal themselves as often as your party. Of course, you can pause the game and use the Retry function to choose the right characters and finish the battle quicker, but there it goes the immersion. Not to mention that during 80% of the first two discs, before the first fight against the Primarch Dysley, the awful decision to leave you with only two members in your party, create a tedious and insipid pace in most fights, not to mention that you just might not want to use the character at all for being intensively annoying (Vanille.)
With all the top-notch graphic quality, carefully crafted sound effects, decent voice acting, except for the dumb redhead, and with the well-timed, if rather dull music; the story, despite its serious approach to a social and political commentary, it just can't achieve matureness with its random melodramatic outbursts of faux-dilemmas of existentialism. What's worse is that none of it makes sense: you don't really know these characters, you don't really know their world, thus we have no idea of their motivations and purposes, unless... and this is the stupidest fault of FFXIII: With all the budget, production value, development time and impressive technology that this game displays, counting the jaw-dropping pre-rendered CGI and the abundant in-game sequences, you still have to pause the game, go to the menu and read text memorandums to understand the story.
It falls on Motomu Toriyama's shoulders the lack of vision and idea, to present this game in a sensitive manner; a lack of focused direction that otherwise would have prevented boring game-play during the first half, an incoherent story that doesn't bother with structure or explanations, and a linear experience that just feels more like dry on ideas.