I watched Final Fantasy VII: Advent Children a couple weeks ago and really enjoyed it. But it was a weird kind of enjoyment, since I've never played a single Final Fantasy game.
No, I don't believe Crystal Chronicles counts.
Being a video game fan, sheer osmosis has given me more than a passing familiarity with the characters... but there is a definite advantage to having played FF7 before viewing Advent Children. Although I thought the movie cool as hell, I'm sure I would have felt a far greater emotional attachment had I personally lived through Cloud's initial adventure. As it was, I was largely watching Advent Children for Advent Children's sake.
I did watch the entire "Reminiscence of FF7" featurette, which hits all the main story points of the game by slapping together edited sections of cutscenes. And even though it is painful to watch old PS1 era footage, I did appreciate the effort. It's funny how FF7 managed to become such an emotional flashpoint game, with its weird super-deformed art style and inconsistent visuals between gameplay and cutscene. Just goes to show how far we've come.
And I'm glad I did watch that, because Advent Children does not do much to draw in virgin viewers. This is quite obviously a sequel. Non-fans are going to have to swallow some scenes without understanding them. To its credit, it focuses almost solely on Cloud, so at the least you're given him to hold your attention, rather than playing to the fans and branching out into all the secondary characters. That is the movie's only concession to non-fans. Barret, Yuffie, Vincent, and the little cat prince dude (WTF?) show up for a big battle scene and not much else.
Once those guys did show up, that's when I realized that, for all the Final Fantasy-style internal angst and torment, Advent Children is really a super-hero film.
The movie looks freaking incredible. It's nice to see CG being used for something other than kid-friendly rubber-stamped pap. The human figures do an excellent job of riding just shy of the uncanny valley by giving some very human-looking bodies a toned-down anime look. Not to mention all the motion capture work. These are not the "real actors" of Spirits Within, nor the stylized plastic humans of Toy Story. I did not feel creeped out by watching them (well, Cid seemed off, but he was the only one). I think this is a new high watermark for CG animation, and it's a shame that comparatively nobody will see it.
Ironically, the very next day after watching Advent Children, I got to the part of Kingdom Hearts 2 where you first meet Cloud and Sephiroth. I'm sure I got more out of that scene thanks to Advent Children, since they talked about some of the same "brother" stuff.