I picked up a copy of Final Fantasy XIII over break (X-Box 360 version), and am currently playing through it. About halfway through (Chapter 7), I'd say it's good, but I wouldn't say it's great.
Story: The game very quickly gives off a cyberpunk vibe that I think is very cool -- recalling the good old days of Final Fantasy VII. I like the plot progression so far, and the story feels novel while at the same time lying well within the Final Fantasy corpus. A-.
Characters: Lightening is a good strong character; one of the strongest female characters I've experienced yet, and the first female lead character in all the FF games I've played. Vanille started off being unbearably annoying, and now exists just on the ragged edge of toleration. For the record, I know its possible to create an irrepressible female character without her being absolutely obnoxious (see, e.g., Penelo), so this is a definite step backwards. And as for Hope, well, I wonder if it is a cultural thing that there has to be a whiny adolescent blond kid in every series iteration. He's always there, and he's always annoying. Other than that, the cast is pretty nondescript. B.
Music: Blah blah not as good as when Uematsu was doing it blah blah I'm old and grumpy blah blah blah. B.
Gameplay: Okay, problem. First of all, this game is linear. Like, even granting that it is a JRPG and a Final Fantasy game, this game is on rails. The levels are not expansive at all, basically involving walking in a straight line towards various monsters -- more reminiscent of Jade Empire than anything. But unlike even Jade Empire, not to mention every other Final Fantasy game, there are no real towns -- just dungeon after dungeon after dungeon. They integrated shops (which you essentially never use) into save points, just to insure the lack of need for towns.
The battle system is pretty good, though I think ultimately a step backwards from the FFXII gambit system. The latter was such a drastic departure from the series, and was so successful, that I'm surprised they didn't stick with it. Speaking of miscues from the last game, the whole bit about augmenting weapons is really poorly designed. For starters, they don't tell you that this is a something you do until quite a ways in. Meanwhile, you're acquiring "components", which for all the world look like "loot" from FFXII that you're supposed to sell off. Deceptive, that is. And once you do start upgrading weapons, the process is quite hazy. You can get efficiency bonuses, but its more guesswork than anything else. Once you start upgrading weapons, it becomes nearly impossible to justify switching to new gear, meaning you're stuck piling on the same old weapons until they eventually transform into something new (I haven't gotten that far yet). It's counterintuitive, frustrating, and a clear step backwards for the series. C+.