Well, my copy of AC Complete finally arrived and I just finished playing the demo and watching the new version of Advent Children.
First, the movie: I haven't watched it in a few years, but it looks absolutely fantastic and really got me in the mood to start the game back up again (I have a half-finished game of FF7 going from last year). I'll probably need to watch it again just to digest everything, but what a beautiful piece of work!
FFXIII Demo: The battle system is great! I really like being able to fire off combos whenever I'm ready, i.e. if I only need a two hit combo, I can just wait for the ATB bar to fill two slots before initiating the attack. I also like the juggling aspect, it reminds me of Star Ocean a bit. Visually, the game is stunning and the CG is on par with Advent Children. Animation is quite a bit better looking than previous games. There's quite a bit more movement animation, which may be interpreted by players as 'lag'. For instance, your character has a turning animation, as well as a start and stop animation.
Lightning is a very cool main character -- probably the best since Cloud, in my opinion.
On the AC Complete set: This is a very nice set indeed. There are two jewel cases with a semi transparent slip-case. The demo case features Lightning seated with sword in lap -- very cool pose, possible international cover art?