I've watched it, and here's my review.
Firstly, let me say I am not an anime lover. I don't dig anime, and the closest I ever got to real anime was the Animatrix (which I loved incidently). So do correct me if I make any wrong statements.
Now, let me just say Advent Children.....sucks. This is an incredible disappointment. I say so because while I had already lowered my expectations a LOT before pressing the 'Play' button. Yeah, I was expecting a lot of over the top action (unfortunately) judging from other viewers' comments but definitely not THIS MUCH action. What makes it worse is that it just has so much untapped potential.
AC's origin as a 20min short is obvious here. Most of the footage as well as the editing is more suitable for a short rather than a 100min movie. The story is hardly fleshed out, and the characters are one dimensional. Not much is made known about the villiains except that they are villians. The editing is so quick that it gives you hardly any time to let things sink in. The movie jumps from one scene to another so much that it hardly has any cohesion. This lack of continuity or 'one-ness' extends to the music. We are given the whole gauntlet of genres here, ranging from piano solos to heavy metal to techno-ish beats to pure orchestral music. The themes are faultless though, since they originate from Uematsu's classic score. It is the presentation that falls apart, literally.
Now, the fight scenes. I can tolerate this over the top stuff (although I have lost the appetite for them some time ago), and even enjoyed some of the duels. Unfortunately, the movie is just filled with them and they are all more or less the same. In fact, the movie so one paced and repetitive it actually starts to get boring after the first 45mins or so. The script also has just too many 'coincidental' situations to be of any value. Characters always happen to be in the right place at the right time so many times its gawdawfully irritating. Lets not start about the utterly lame and contrived 'Old Gang Returns' as well as the 'Boosting Cloud' sequences. And why did Cloud somehow survive that blue fireball Bahamut shot at him? I am so suprised at how low Nomura stooped in the name of fanservice. Cloud's moment of glory with his Omnislash was so reminiscent of Ultraman's weekly antics (where he gets pummelled until his chest light beeps before unleashing is uber power) I burst out laughing.
So much for the bad stuff, what about the good? Well, some scenes did have magic in them and some of the music like the summoning of Bahamut, Kadaj's demise, Finale and end credits suite is classic. Of course, needless to say, the CG is top notch though I never understood the effeminate men craze Japs have.
Bottom line, this could have been a great short, instead it is a disappointing movie. Not better than Spirits Within either. Strictly for the fans, no, strictly for the hardcore fans. 5/10