That looks really good what show is it from? It looks a bit blurry in places is it supposed to look like that? And the thumb on his hand is red is it blood? If it is it needs to look a little bit more like blood. Also get rid of the stars on the border line it doesn't look right. Anyway, you've done really great job on this wall! Good luck!

There are several issues with this wall, the most urgent of which are:

- chopped-off scan
The scan you used does not show the entire character, Kamui has got his elbow and his feet chopped off, and that is unsightly. You could align the scan to the bottom of the wall to solve the problem with the missing feet, but for the elbow, you'll probably need to do scan extension and paint it in by yourself. Considering this is your first wallpaper, this may be a bit hard, so if you don't feel up to it maybe you should be looking for a better scan to use instead.

- extraction
The extraction of Kamui from the scan is poorly done, with a lot of jaggedness and little specks of the background remaining. To do this properly please see these tutorials:
http://www.animepaper.net/group/designdepot/discussions/30374/
http://www.animepaper.net/group/designdepot/discussions/30234/
http://www.animepaper.net/group/designdepot/discussions/30346/

- background
You have these rectangular blocks of various patterns, and then starry sky top and bottom, which are not working together. Give a bit more thought to what you want to do with the background. Some tips from the wallpaper guide:

wallpaper guide

Is the background done well?

If you just used a few Photoshop filters you need to invest more effort. If you just used a gradient or a solid colour, that's probably not good enough.

If you just used a stock or you took a stock and used 1 filter, that's also not really good enough. The background is generally the area where you get to shine when you make a wall - try to really put some effort in.

Good luck!