I'm about 3 hours in as of now. So far, it's all good; it raises the bar for videogame production values, acting as an "Avatar" of sorts for videogames.
As for the linearity, while it is more linear than FFIX and earlier games in the series, honestly, I think people may have been exaggerating, as the level design is no worse than FFX's (And FFX was an awesome game).
The battle system is just as I expected it to be; ATB perfected. This is, without a doubt, one of the most fun and engaging battle systems in the series; it is true that you can only control one character during battles, but that is a minor issue that really doesn't detract from the experience at all.
As for the cutscenes, some people were saying that the game was incredibly heavy with them, calling the game a "movie" of sorts; so far, this seems like bullshit. The game is no more cutscene heavy than FFX was (And FFX was an awesome game). I like the way the game handles cutscenes, as well; the cutscenes are shorter and more scattered around than other games that elect to just put out less, but far longer cutscenes (I'm looking at you, MGS4).
There aren't any towns, but honestly, I can't say that I miss them. Since when did an RPG need "towns," anyway? In some situtations, they just feel too artificial and non-fluid; in a game like FFXIII where you're seen as terrorists and pretty much hated by everyone, honestly, being able to walk around towns and in to random people's houses and shops would be stupid and completely take you out of the game's atmosphere and plot. Having no towns can really add to the atmosphere, as well; in Metroid Prime, there were no friendly NPCs and everything wanted to kill you, which made it feel special. In Demon's Souls, aside from the Nexus and the odd merchant placed here and there, there was little to no human interaction whatsoever (Adding to the overall feeling of hopelessness the game possessed). In FFXIII, you're outlaws being hunted down by an autocratic, highly religious government. It works.
Speaking of plot, so far, the game's narrative and characters (Save for Vanille, who is really starting to piss me the hell off) are far more interesting than XII's. This is a true step up, and a return to form for the series. And that's without mentioning the lore of the world of Coccoon and Pulse; overall, it's a very interesting setting. Let's see if the rest of FFXIII's plot can make the most out of the setting.
So yeah, overall, so far, so good. The way FFXIII is structured, however, brings to mind a theory that I've often considered; that the video RPG genre is slowly going to die as other genres adopt RPG elements and hold better-developed stories, making "true" RPGs harder to distinguish. FFXIII is a more streamlined experience, with a greater focus on combat than some of the previous FF titles in the series, which had the occasional puzzle in addition to combat. Overall, it's a very experimental title (Of course, then again, the FF series is a more experimental series than most other JRPG franchises).