I give it an 8.5 out of 10. It's good for the most part except for the poorly planned and poorly pieced together storyline.
edit: Here's a review I posted for it on another forum I go to (minor spoilers):
Pros:
The Visuals. Holy crap, the computer graphics are awesome. From the beginning to the end, the whole thing is just like "wow". The ending credits are the best, showing a montage of backgrounds and visuals that just leave you thinking "Holy shit, those aren't real?"
Most of the characters. I liked the handling of a lot of the characters they did here. It was interesting to find out that Rufus and Tseng were both still alive after what happened to them in FF7. Reno and Rude made excellent comic reliefs for the most part, especially Reno. Kadaj was a cool character too. The voices for the most part really fit each character well. I liked some of the voices I'd heard before, such as Tooru Ookawa as Rufus Shinra, who was also the voice of Roy Mustang in the FMA, and Keiji Fujiwara as Reno, who was the voice of Maes Hughes in FMA. And also will be the voice of Axel in the Japanese version of Kingdom Hearts II. He's like the trifecta of awesomeness. But anyway, yeah. That was all cool. The only voice I thought didn't really fit the character was Barret's. The rest were perfect.
The action. The action sequences are fast-paced, frequent, and amazing. My only complaint about them is that the battles with Yazoo and Loz get really old really fast. The final battle with Sephiroth is amazing.
The music. Holy sweet Jesus, the music. Nobuo Uematsu reprises his role as the music composer here, making both remixes of old FF7 tracks and brand new ones. The music perfectly sets the mood throughout the movie.
Cons:
The plot/storyline. It's there, but it's just really hard to understand. You'd probably need to watch it through a few times to fully understand everything, but even then, it just feels poorly planned and poorly pieced together, with very little explaination for how or why certain things happen. It feels more like an anime plotline rather than a well thought out and intricate Final Fantasy story. I do like how they worked Materia into the plot, though. Now we know how equipping Materia works.
The other characters. All right, what did they do to Marlene? She acted much more mature in FF7 than she did in the movie. And it takes place 2 years later. And I still don't understand what the point of Denzel is. He's just some random kid who happens to be friends with Marlene and has no real importance to the plot. Why focus so much on him? Also, most of the FF7 part members like Barret and Cid kind of get pushed out of the spotlight. They have like one big battle sequence and that's it. Also, why give Cait Sith and Reeve two different voices? They're the same person aren't they? And what the was up with Red XIII? They only gave him one line in the whole movie, and it wasn't even a very good one.
Despite the fact that the plot sucks, the movie is still awesome for the most part. Madness gives Final Fantasy VII Advent Children an 8.5 out of 10.