Anime Watch it for the fight scenes and nothing else
The story and the characters are awful (especially Cloud not only losing all his character development and the game absolutely shitting on the themes of FF 7 just because someone at Square desperately loves emo man children) but at least the fights and music are great.
And that's pretty much all that can be said. The writing quality is less than you would expect from a fanfic but watcha going to do?
Anime Advent Children: Pure Fanservice
Due to the humongous popularity of Final Fantasy VII, it's natural that Square would succumb to the temptation of milking the name for all it's worth. This is not an outlet for critiquing Square's business decisions, though. Nonetheless, it gives you an idea for what Advent Children is about. It's got a strong summer blockbuster feel with fantastic animation, awesome action scenes, and is jam-packed with fanservice for those who've played the original game. However, like most summer blockbusters, that's all it really amounts to.
The plot is something I can sum up in a nutshell: Sephiroth gets revived so that he can have an awesome climactic battle with Cloud to an equally Crowning Music Of Awesome remix of the iconic One-Winged Angel. The rest is mostly an excuse to get up to that point, crammed with action and angst. Yep, angst, what some may refer to as a Final Fantasy staple. Kadaj, who is pretty much "the guy that will turn into Sephiroth", whines constantly about Mother, or Jenova. Cloud for much of the movie is unable to get over his past, though you have to hand it to Tifa for doing a Lampshade Hanging and telling him that it's not all about himself. People claim that I probably should play the original game first before critiquing the plot, but I counter that a movie should be able to stand on its own for newcomers to the series. Also, from what I heard, people that have played the original were still unhappy with Cloud's perceived Character Derailment, but I'm not going to waste too many words on idle speculation. Admittedly, I might be able to appreciate this movie more if I played the game first, but from what I've seen, I doubt that knowledge would make it seem any more than pure fanservice, although I might be able to get said fanservice, which is worth something at least.
If you're looking for a nice animated action movie, you've got it here. Just don't go in expecting too much depth.
Anime Less Than the Sum of Its Parts
Final Fantasy VII Advent Children is a glorified tech demo. Its plot is completely incomprehensible without having played Final Fantasy VII first, and even then it is frustratingly vague. All of Cloud's character development from the game had regressed, new villains are introduced out of nowhere with no solid explanation of their backgrounds, seemingly dead characters are revived for no apparent reason, and Sephiroth is resurrected for absolutely no good reason. The dialogue is horrendously bad, the characterization is non-existent and what is comprehensible in the plot is riddled with massive plot holes.
The up side? The movie looks and sounds fantastic with ridiculously good CGI visuals and a great soundtrack by Nobuo Uematsu. Really, the movie is nothing but a giant, lovingly assembled pile of Fan Service. If you are a fan of Final Fantasy VII, and that's what you want, you will be happy. If you want a storyline that can stand on its own two feet, makes sense, has strong characterization and adds anything meaningful to the already existing storyline of Final Fantasy VII, you will be incredibly disappointed. In other words, the movie exists solely for Rule Of Cool. If you are Okay with that, you will enjoy it. If you are not, don't bother.
Oh, yeah. Any scene that doesn't involve over the top action is filled with either nonsense exposition or wall-to-wall Wangst.
If none of that scares you off, have fun.
Anime One of the greatest video game movies of all time
(Review is for Advent Children Complete, Japanese subtitled version)
And yes, I mean it. In an Overly Narrow Superlative sort of way. To be honest, I wouldn't even call it the greatest, since at least some of the Pokémon movies can work as standalone movies. And Wreck-It Ralph? Don't make me laugh.
That said, Advent Children Complete can be a blast. Of course, it depends on your expectations. For starters, basic familiarity with FF7 and its mechanics and storyline helps a lot to understand what's going on. Secondly, don't come in expecting an amazing animated film; come in expecting a loosely serviceable plot as a vehicle for amazing animation, fight scenes and music. I hear complaints about the characterization and dialogue in this film, but hell, that's why I watched the Complete version (watching it in Japanese helped with the dialogue issues, though my choice was more due to Cloud speaking Japanese in Super Smash Bros. than anything). Fixing Cloud's character was one of the biggest problems they addressed, and he gets a half-decent character arc and lots of heartwarming moments this time around. Not to mention that the Cloud vs. Sephiroth fight scene alone is worth the price of admission, and probably the best fight scene I've ever seen in an animated film (another Overly Narrow Superlative).
Overall, my expectations for ACC were somewhat low, so I was pleasantly surprised. Like so many other people are saying, it works as a glorious piece of FF7 fanservice as opposed to a genuinely good movie. So many things in the film reek of Nomura being more used to directing games than movies (right down to the two-phase "final boss"), and I have a feeling Advent Children would have come across better if it was instead released as a "Final Fantasy VII-2" game with the plot of Complete from the beginning.