I've seen a few vocal people discussing Final Fantasy XIII and how it's gone in a "bad direction". I've even seen one person blaming the merger with Enix for the direction FFXIII went in. I couldn't disagree more. It seems to me, given the history of Final Fantasy, that FFXIII is the result of sales trends, which is also, of course, the simplest explanation for why it is the way it is.
 
Basically, I propose that sales trends in the series are what has driven FF in this direction.
 
Hironobu Sakaguchi, the original creator of FF, left Square to create Mistwalker after the bomb that was Final Fantasy: The Spirits Within and the poor performance of Final Fantasy IX, which was his baby and which was overshadowed by FFVIII in both reviews and sales. FF:TSW was an utter bomb and remains one of the biggest cinematic financial losses of all times while FFIX remains on the bottom half of most "top FF games" lists and remains as one of the poorest selling FFs of the post-16bit era (actually, I believe it had the worst sales of the post-16bit era).
  
Here's how things went with Final Fantasy:
 
After FFVII was a success, Square decided to break the FF team into two groups that would simultaneously work on the next two games in the series. This was well before the Enix merger. 
 
The team that created XIII is the team that brought you VI, VII, VIII, and X led by Yoshinori Kitase, and I think it's pretty obvious that XIII is the spiritual successor of these games. Look at the character archetypes and the style (both graphically and gameplay-wise)... the characters are almost uniformly taken from FFVIII, and the battle system is clearly inspired by these past games with a blend of VIII and X's systems. The Crystarium is just a new version of the Sphere Grid from X.
 
In The Gooch's (read: Sakaguchi's) absence, Yasumi Matsuno of FFT and Vagrant Story fame took over FF12 only to relinquish production to Kawazu of the even less well known SaGa series when he fell ill. Despite all these problems, the game turned out pretty well and was critically acclaimed, but the sales fell pretty far short compared to VII, VIII, and X. That said, even though Team 2 headed up production of FF12, it was inspired by the original desires Team 1 (again, led by Kitase) had for FFX in regards to an open-world approach.
 
Now take a look at sales historically and you get an image of why FF has gone this way. For reference, sales peaked with VII and were nearly as high for VIII and X, and X-2, a  game that cost almost nothing and had a very short development cycle, did fairly well also . Meanwhile IX and XII had significantly lower sales.
 
Is it any wonder, then, that FFXIII is basically a natural evolution from these particular games? Of course not. It's not surprising at all that the open-world nature of XII, for example, was abandoned after the game had low sales despite high critical praise. In its place is a world that's at least as constricted as that in FFX, which had just as high critical praise but significantly higher sales, with battles and characters more akin to that of FFVIII's, which had even higher sales along with high critical praise. 
 
I'm not reviewing the game yet because I haven't finished it. I can already say it's not my favorite in the series. But I predict sales of FFXIII will be quite high despite the complaints from many of the Hardcore Jaded Old-School Lamers (HJOSLs) out there that it's a bad game. After all, if nothing else, everyone basically agrees that the visuals are some of the best in a videogame ever, that the music is good, and the gameplay is at least tolerable. Plus, it's the first FF of this generation--you know it's going to be a big seller just because of that.
 
I think the real interesting caveat to FFXIII is the decision to co-create FFvXIII simultaneously, and to see how well FFvXIII sells once the dust settles from FFXIII. This is the major change made in FFXIII over the past games. FFX-2 was SE's first foray into this kind of development cycle, and it actually worked quite well for them, so we'll see how it pans out with this game.