It's not like VII, VIII or even IV were any less linear. I really hate this 'no world map'=linear argument. Also linear does not equel bad.
The cast is great, but to each their own I guess. It's probably the last time an FF game had proper FF-like characters and not boring underdeveloped characters (FFXII) or anime inspired characters (FFXIII)
The world map gives you a positive sense of exploration, rewards you with places to go, and opens up the more you go through, especially as you get the boats and then the airships, giving it a good sense of progression. It's a tried-and-true formula for a reason. Calm Lands/ Gran Pulse are basically a world map, except they are restricted to a certain point of the game, and there's nothing to do besides that point, outside of a few endgame bosses. And let's not even talk about transforming every single map into a road: it feels unnatural, and needlessly restrictive. The idea that of taking good gameplay elements away for the sake of "better storytelling" was nothing more but a(n old) vision of a director that keeps failing at keeping most of his audience interested.
Also, FFXIII's characters have more screentime than FFXII's. They do not have more development. Let's not confuse both.
Hope has basically the same development of Vaan, but spread through two times the cutscenes for the sake of bad melodrama and filler. Technically, that makes it worse, because at least Vaan faded into the background and did not annoy the players. Also, Vaan's development, outside of being almost exactly the same as Hope, was also more believable and logical. The situation with Reks was carefully crafted, both by the writers and by the characters who caused it, so the decision to trust Basch against the last dying words of Vaan's brother was an actual dillemma. Vayne had crafted a clever plan to give the illusion to the Dalmascan people that they only fell as hard as they did, because of their own people; that everything could have been better with "negotations with the Empire". This softened up Archadia's negative image to the Dalmascans, and is what made Vaan's dillemma plausible.
Meanwhile, Hope's mother deliberately decided to fight in front of his son against a government that was purging them out and then killing them out, in from on their own eyes. Hope was there the entire time, afraid of that government's army, and when she dies by the army's hands, he spends
half the game blamming Snow, whining about Snow, and the writers even unbelieveably exaggerate that up to the point where Hope wants to
kill, kill, kill Snow, only to come at the sudden, extremely obvious conclusion that it was the goverment's fault all the time, concluding a very forced, a very poorly-written character arch in an anti-climax.
And then Hope becomes an internet motivational-speech bot generator, except when his character arch goes suddenly back for no reason other than so he could get his eidolon doll. The big problem with Vaan, is that Vaan disappears from the plot and becomes pointless after that.
Lightning is terribad. She only matters for an early subplot, like Vaan. She fades out of the story once the subplot is resolved, like Vaan. And she is poorly-written, like Hope. Her development is a mesh of her stereotype and Ashe's character arch, told in two-three cutscenes through monologues, which is a pretty terrible form of storytelling in this case (and FFXIII is full of this, like Cid's character development). Regardless, whatever little character development she had, was either pointless in the long run, or completely ignored and contradicted for the final act and the sequels.
Fang is nothing until her sudden arch before the final boss, Sahz actually has believable characterization until the writers start contradicting themselves of grossely exaggerating for the sake of drama, making the drama feel very cheap, and for Snow, whatever development he had (was it during Hope's arch?) was completely ignored right after.
Finally, we have Vanille, who is the single most important character in the game, and no one notices it unless they analyze the story of FFXIII, because she spends half the time acting in possibly the most exaggerated way I've ever seen her stereotype act, at the middle of holocausts, as if she was completely psychotic. But then again, so was Snow, so was Sahz, so was Hope, so was Lightning. They are all more psychotic than what the writers wanted them to be.
And let's not even talk about side-characters, shall we? Because in that department, FFXII was surprisingly good, and easily the single best main FF at developing side characters. Vossler, Cid, Gabranth, Marquis, Larsa, the Occuria. The only other time I've seen such a likeable cast of side-characters in main FFs was in VII, with the Turks, the Shinra, Hojo, Sephiroth and Jenova, and those were not as well-developed generally. FFXIII is, in contrast, a laughably mess, ranging from generic plot tools with unbelievable, sudden changes of heart (Yaag), to dry characters that suddenly reveal wasted potential through boring monlogues (Cid), to plot tools with some potential that get trashed in the most insulting way a writer could do it (Jihl).