Yayz, first coment!
Congratulations to your first wallpapaer, as you see, hard efforts always pay up. You did a good job on the color matching (blue was the only right choice) and the character looks clean.
What could be better: First, the resolution. 1440x900 is really the minimal here, at least 1680x1050 and 1920x1200 for optimal. Sure when the character is not vectored, it's hard to resize without loss of quality, but you know, bigger is (always) better XD
Also this abstract style should be match more to a happy chibi style and the Colonel looks very serious in this(or morally bankrupted :P)
But still...for a first try is more than good and you wil be better and better with every wallpaper. I'm sure of that and waiting for your next work.
+Fav