I think the best AMVs are ones where you can tell the editor tried really hard to make it good, and that they enjoyed making it. There's a lot of videos on sites such as *cough* You-Tube or Myspace, where the editors have said stuff like ''I made this video because I was really bored'' or ''This only took me an hour to make'' and strangely enough, not many of them are that good. These people are obviously missing the point - you can't make a good video in an hour or two, most good videos take days, months or even years to make. You don't make AMVs because you're bored, or to try and be 'cool' - you make AMVs because you want to and you enjoy making them.
The editors of most good AMVs I've seen have said things like ''This video took me a long time to make, but it was worth it'' and ''I really enjoyed making this AMV'', and the time taken to make it a good video really shows. I enjoy watching anime music videos where you can tell how much fun the editor had making it. No matter how crappy the quality might be, or how fancy or plain the effects might be, what I think makes a good AMV is the fact that whoever made the video really tried hard to make it as good as possible, and the time and effort put into it really shows.
So anyway, I'd like to hear all your opinions on what makes a really good anime music video. Feel free to rant if you want.
