Review:
Story & Characters: I won't go into detail on what you already know. 2 years after the original game events, an illness called geostigma torments the people, and with no hope in sight they look towards a man who gave up being a hero to live in solitude, Cloud Strife. Now as far as the stories concerned, you will most likely be lost if you haven't played the original game. Certain elements attempt to touch the fabric of the original game but never really help you understand why.
Hell to be honest, if you haven't played the game more than once you'll still be kind of lost. But to be true to the story, the characters were pretty good. The attitudes that everybody had in the original game are still here. Cloud becomes a cold loner once again, Reno is comical and a badass as he ever was, etc. etc.
The new characters were odd yet believable that they were just soulless and completely destructive. Over-all the story was very nice, bad sadly seamed to end a bit too soon and still does not quite explain a lot about the ending of the first game.

Art: The character designs are completely astounding. Being a 3D art major in college, I've learned to appreciate good work and this most definitely was astounding. "Final Fantasy: The Spirits Within" was just one technological advantage, this one takes it to the next level. The animation is flawless, the characters are detail-for-detail amazing, and the world (backgrounds, people, trees, etc.) are truly unbelievable (in a good way)! The monsters definitely felt unreal and devastating. After watching this movie you can't just wish they would remake the original Final Fantasy VII game. A graphical upgrade is one thing, but a complete overhaul with modern technology is on a completely different level of greatness. The costumes were very refreshing and the detail still makes my mouth drop down. The weapons you just can't believe.
The mechanics scheme of Clouds new sword was just eye opening. Being a fan of the original game (practically playing it to death) the art was definitely a change of pace for the best. Sadly, for fans of the original game, Cait Sith has given up the huge robotic mog for riding on the back of REDXIII. The 3D is the best well see for years to come and is only a milestone of what technology is accomplishing.
Do not associate this with Finding Nemo, Monsters Inc., A Bugs Life, and whatever full 3D movie is out there, this has definitely raised up the bar in what 3D action movies should look like (with the latter only being Final Fantasy: The Spirits Within). Some action scenes maybe totally unbelievable but are completely flawless in terms of character animation.

Final Fantasy Advent Children is so far the best videogame and the best animated movie ever made.