You know what, I enjoyed this pretty well. I had a few issues with it, but in general, I think you had a good [and focused] concept and executed it fairly well. And a good/focused concept will get you places.
The first thing I'd like to point out is that you really shouldn't watermark your videos like that. It's ridiculously distracting and takes away from the enjoyment of the videos. If you do want to watermark, make it invisible or hidden to the naked eye.
Next, I think your scenes could have used more movement and far more cuts. The scenes lasted very long and could have used some more cutting and hitting with the mood of the music. Like at 1:07, when the music begins to change its tempo a little, and you've still got the same scene playing, and its a very static image.
The inclusion of L and the FBI cops kind of hurt your concept. Up until that point, I thought that you concept was about Kira's world and his obsession with godhood and making his judgement throughout the world, and you'd kept a lot of good focus until that point. When L and the cops gets introduced, it's sort of just a little odd to see them so suddenly introduced, without much context for it. A scene showing them investigating Kira would have provided that, and given him a reason for killing them off.
Lip flap, or the act of talking when in the middle of a scene without it begin intentional lip sync, was a problem at times. This can be masked out, especially in the scenes they had/were in.
The flashback scene at 2:26ish is totally out of context and was weird to see. People who haven't seen the anime will not really understand why he's spazzing out.
But on the whole, it was pretty well done for a first AMV. You did a lot of things right, and I think you did a generally good job with it. I think more experience in the field will help fix the issues I mentioned, as its things that editors learn in time as they get more AMVs under their belt.
Oh, and MAJOR kudos for reading the announcement rules and announcing your first video properly.
Nice work, and welcome to a-m-v.org!