First things first: I'm going to call it Final Fantasy 13 throughout this entry, because I don't want to keep typing out Final Fantasy XIII. The latter is more letters, and it's easier for me to leave off or add an I by mistake and inadvertently refer to another game. If you don't like it, well, too damn bad.
Also, it goes without saying that this entry has massive spoilers on the game, potentially. If you've held off on playing this game even longer than I have, well, please don't read this entry.
Anyway – As the title of this entry implies, I was a fan of the game. On the Internetz, it gets quite a bit of flack for being far more linear than previous games in the series, but I looked at this aspect as a positive.
Without 20 side areas and towns to explore between missions, I felt the main storyline had more of an urgent feel than past games in the series. For example, in Final Fantasy 6, you're threatened with the idea that Kefka can strike at any time... Except that you can literally spend 100 hours fighting dinosaurs, exploring castles buried on the ocean floor and fighting ghosts in your characters' dreams, and nothing bad will happen.
(I feel like a developer could make a ballsy statement by offering a “real-time” mode in a game. i.e. If you don't beat Final Fantasy 15 in 100 hours, then the bad guy does win. Just make an optional mode that you get an extra trophy for, or something. The Persona games kind of limit you with a certain number of days to get things done, but this affects you much more when it comes to social links, not battles.)
For the first 20 to 30 hours of Final Fantasy 13, you are on a hard-wired path that I found pretty interesting. You're mostly focused on staying alive, either by running from the people out to kill you or by attacking their headquarters yourself. In this respect, I found it somewhat similar to Final Fantasy 2e / 4j, which forced you to have certain parties and characters with well-defined traits.
Once you get to Gran Pulse, the game does open up a bit like the World of Ruin in Final Fantasy 6, and all the presentation values truly shine. After spending your first 20 hours in confined areas and a steampunk environment, it's incredibly refreshing to see 250-foot tall beasts stomping around the plains. (It's also neat to see that there is a vague sort of ecosystem at work – You'll see beasts that dislike each other attacking one another. I think they should have pursued this angle more, actually. You can watch them fight for 10 minutes, but one side won't ever actually win, and creatures are always in the same spot.)
Of course, once you get there, you run into another common complaint – Half the crap you run into can kill you very, very quickly. Final Fantasy 13 makes it hard to level-grind by not re-spawning enemies easily. For example, if you just beat a group of enemies that drops something you can sell, or that gives you a good amount of experience, you either have to save-and-load or venture well off screen to get them to re-spawn.
If you're someone who loves to over-power enemies, then this is incredibly frustrating. You don't really have the opportunity to get super-powered until 75 percent of the game is over. If you're like me, and mostly playing just to enjoy the plot and not engage in fetishistic item collections, then you're perfectly fine with the challenge most of the game presents.
As far as the story goes, I thought it was one of the better ones. They took some very un-Final Fantasy-like risks with it, which I think I appreciated more than others. Examples: People already in love, as opposed to falling in love while the world is ending. Popular people capital-D dead instead of being revived. A woman is legit the bad-ass of the story, and she's not some weird lady with a short haircut and mannish appearance (sorry Paine). A story told with some interesting flashbacks. Characters who have done legit bad things – like punching a hole into a world – in the past. Not taking the easy way out with the ending.
However, I will say that I wish they'd up the ages on some of the female characters. Now that I'm 27, it feels... creepy. Even Sazh is caught leering at Vanille, who is pictured below:
She's dressed like that for the entire game. Oh, did I mention that she's 16? yikes. It's awesome that Final Fantasy 13 had two awesome female characters who basically kicked ass and took names later, but a bit of that is unraveled when Miss Lolita 2010 is also on display.
When it comes to young, female characters, I sometimes feel like the Final Fantasy developers do nothing but watch Hayden Pantiere, Hilary Duff and Miley Cyrus tapes. To close out the post, here is their idea of an appropriate 15-year-old as featured in Final Fantasy 10:
The picture of Vanille is from this site. The Rikki and Light images are from a bunch of random forums.