I'm late to the party as always -- I got FFXIII a little while back. So far I've played about 14 hours. A lot of people are complaining about the game, but I quite like it.
I'm not a huge FF-nerd; I haven't played a lot of the older games, like really played them. The only ones I can think of are FFIV, V and VI on the SNES. And I used an emulator. And I cheated...
Compared to the older games, FFXIII is very linear, or at least have been for most of my 14 hours. Some of the enviroments can get a little boring because of it, but so far, for the most of it, that hasn't been a huge problem. I actually kind of like knowing where I'm going for a change.
Another thing I like a lot compared to the older games is how when you die, instead of being returned to the title screen (which pisses me off to no end) you're prompted with a dialogue asking if you want to retry the battle. It brings you back to the very moment before engaging in the battle, meaning you can adjust your gear or spend Crystarium Points or whatever before attempting the fight again. Very nice.
It supposedly takes 50+ hours to beat the game. Knowing me - and I do know me - that's probably closer to 70+ hours... So far so good though. :)