I just beat the game a moment ago.
I enjoyed the ending quite a bit. It wasn't particularly unpredictable but it was a satisfying conclusion and made me feel a bit for the characters, which is something the game hadn't done up until that point.
Overall though I think the game was fun but flawed. It could have been so much better with just the inclusion of a few towns or population centers to actually flesh out this world that I was supposed to obviously be invested in, but wasn't. I really do hope the exclusions of towns and interactivity with the world isn't a permanent change to the series, or else it will simply never achieve the heights that it has in the past. No matter how nice the cinematics are (and they were really amazing, here, to be fair), they can't compete with the feeling of actually exploring and interacting with the world.
Then the point does come in the game where you are given freedom, however when this happens the story almost completely gets put on hold. There's no reason why you can't have a good story with exploration, something the designers didn't seem to understand.
But my feelings on that are by now well known. I still felt that the story was rather poorly told. It's near impossible to really understand what's fully going on without more or less pausing the game and reading the datalog for a long time. There are some things mentioned in the data log that seemed of great importance but that were barely even mentioned within the actual plotline during the game. Having a datalog is a nice inclusion if it's to supplement the plot, but relying on it almost completely in order to understand what is going on is simply not acceptable.
However, despite my constant complaining about this game I did enjoy it quite a bit. Just not for reasons I expected. I really loved the battle system. It just got better as the game went on, becoming more challenging and strategic. This is the first FF game where I actually continued to play FOR the combat, rather than the story (except for FFXII, which I played just because I felt like I should). I would actually be perfectly happy if they just held this battle system over for the next game. It's that good.
In the end, like I said, this game does place somewhere in the middle of the pack of the series. My ranking would be 6>7>10>9>13>5>4>8>12
Woulda been higher with towns.
http://www.escapistmagazine.com/videos/view/zero-punctuation/1569-Final-Fantasy-XIII
Zero Punctuation's review of the game. Quite funny.