As someone who has never really played any FF game, I just picked up FF XIII and I have to say that I am enjoying it quite a bit.
The linear aspect of the game that annoyed most people actually works for me. It allows me to focus more on the fantastic fighting system and the game's enjoyable story.
Just about the only gripe I have with the game is the stupid character names, which I've been told are a recurring theme in some FF games.
I mean seriously... all the random letters and words you could come up with and they name the main character Lightning and then there are the fal'Cie and l'Cie. I can get by the main character having a silly name, but the latter names are just ridiculous every time you hear them said...