I just made this a few days ago, and I'm not sure if I should add more or not. What do you think?

http://img135.imageshack.us/img135/7314/deathnoteum9.jpg

I liked, but i think that the background is too simple... try some textures

Although quite complex, this wall is highly stylized and depicts an original viewpoint. The colors are wonderful, and I really liked the layout with the spacing in the middle. It draws the eyes well to both Light and Mello. However, since there are so many characters in this wall, I think it was overkill to have black-and-white shadow images of Near and Mello (and Light, to a much lesser extent).

My favorite part of this wall is Light's heart, except that it's too far to the left side (of the wall) to be in the correct place for a human heart. The heart, the crosses and the washed out character outlining gives it a very "William Shakespeare's Romeo and Juliet" feel (you know, the one with Claire and Leo).

I also like the lettering, but would make some small adjustments as to their positioning. For example, I would have Misa's name curving around her head (right now, it's more over Light than Misa), while I would have Ryuk's curving around those feathery things on his collar. I really don't like that his name appears on top of the image, like it's stamped on his forehead.

Also, Near is a little too washed out. I realize that the character wears white and has white hair, but perhaps you could make his clothes more of a pale blue. Just a suggestion.

The apple is a cute idea, but it's too bad the cross covers it up. If you remove the overlapping cross and the "death note" lettering from the top left cross, the wall would have a clearer effect overall, I think.

There are some really great ideas here and the majority of the execution is great too, but what stand out about this wall the most is the stylization. Keep up the good work!

You need to either make your different style blend in nicely.. or you should try to stick to a specific style.
In this wall, nothing seems to blend well with the other elements.
the background colour and style isn't all that good.
the text doesn't really work all that well
the design at the bottom is too random and doesnt fit in because of the colour scheme and style
you should check out other users' wallpapers and see how you can improve.
for now, this wont do... even though it is a good effort
keep working! you'll get better! :)

Hm... looks like a scan abuse, they just take too much space. Usually it's hard to make a wall with so many characters... if I were you I'd choose one or two. ^^
Hope that helps clear things for a start.