I watched Advent Children last night at Nosefoot's/Zor's place and I've gotta say, it wasn't that great.
Sure, the graphics were fucking AMAZING, but the movie as a whole wasn't very entertaining if you're not familiar with every single fucking aspect of the game, like me. I know the basic storyline, so I at least knew who the characters were, but other than that, I didn't know anything and that really made the movie pretty boring.
I feel like movies should be able to be good by themselves if they're going to be based on something else. I'm not saying that every single plot device has to be explained, but it should still be entertaining if you aren't familiar with the previous material. Sure, this movie's great if you can name Cloud's attacks as he performs them and stuff like that, but if you can't, you're out of luck and shouldn't watch this movie.
Basically, as a movie for gamers, Final Fantasy 7: Advent Children is 10 kinds of awesome, but as a movie in general, it's only so-so.
That's my opinion and I'm sticking to it.