I hope the quality of what I'm seeing above is a rough draft. it looks really pixelly and I can tell you now the colors will blind people. If you're going to put a bold border on that ghost image behind him, be sure to incorporate the bold lines elsewhere on the wallpaper. Perhaps on the sun ray stuff.

If you add text, easiest spot is right side, center.

For text I would select a memorable quote from the anime, either something that Alphonse said himself or was said about him. Example: "Humankind cannot gain anything without first giving something in return. To obtain, something of equal value must be lost. That is alchemy's first law of Equivalent Exchange. In those days, we really believed that to be the world's one, and only, truth." It fits him because he is proof of it. As for font purposes to fit with the amazing look of the ghost image you could try either something thick and bold or you could go with something thin and elegant to complement Alphonse himself.

Nice work so far, maybe less pixelated, and it would be perfect.

~GeroGirl

At the moment, this looks very rough, a bit like it was just cut out from an anime cell, and placed on a Street Fighter II screenshot. I think a bit more cleaning and work on the background would do wonders.

This wallpaper is surely lacking some work on the background. I would recommend to change it entirely. What was your real purpose with it?

For the shadow-ghost stuff I'm not sure about it... I'm not sure the gradient ending in white on top is the best choice. Especially if you have that black or dark blue border all around...

If you're looking for more contrast, get ride of the background but not the idea of it. Keep the concept of the lines-lightnings coming from the same point but create it yourself instead of getting it from a bad looking source. Start with black (or dark blue) and white en maybe you can tone down the contrast if you feel it's too obvious by using two kinds of gradient in the lines.

For the text I would indeed take a quote like GeroGirl said or the logo. But if you choose a quote maybe take something a little bit dark cause it's a scan where Al really looks sad and on such a bad mood...

You also shouldn't leave Alphonse "flying" into your wall. Give him something to make a connection between the background and himself.

Anyway good luck with this and don't hesitate to post here your next version! :D