Okay, first off, I'm a little angry right now so if I make a mistake, don't crucify me for it. I'm just going to point out (at least with rock music) the process one has to take in order to make a good AMV by looking at the parts.
To start off with this ranting, the most important part of making an AMV is matching the contents of the AMV with the choice of music. Let's say you use a rock song; does it have a fast beat, slow? Is the tone sad? Excitable? You have to be able to match the content with the aspects and tone of the song. If its a sad song, then use content that invokes emotion. Don't just use the opening and ending sequences of the game for the AMV, especially the same parts over and over which brings me to my next part of this: repetition.
Using the same parts over and over multiple times drowns out whatever meaning the AMV is supposed to have especially if the way it is used is almost the same each time. Two or three times you can probably get away with if you use the same bit in three different ways (e.g. the second play more of the segment after the one you use by a few seconds).
Here's an advisory: when using fast-paced (or mildly fast-paced) rock music, don't expect to get away with large clips! Because of the faster pace, larger clips will bore the audience. Sometimes, you will have to use shorter clips that may only be used for a single measure in the music. If there are parts that feature the artists screaming their lungs out, use clips of something big happening on the screen. Also, whatever clips your using should somewhat match the movement generated by the music. If there's fighting, it shouldn't be durin a slower or more mellow part of the song. You have to be able to match changes in the music with actions on the screen.
At the end of most of these songs are a run up to the big finale. You can accomplish the mood of the impending finale by using almost all short clips. These should be parts of action sequences to keep the audience energized to the very end.
If people could manage to put in the work to make an awesome AMV (at least for KH) I wouldn't have to make this rant. But someone has to do it.
Goodnight, and goodluck.