I think you need to learn to use gradients, shading, textures, brushes, etc... Even your use of the airbrush has to improve if you want to achieve a decent result, although it's easier said than done and I never got to master those tools when I was into that stuff. If you need inspiration I would recommend you read some Ultimate X-Men or, if you are more into manga as it seems you are, something by Udon, the guys behind the Street Fighter and Darkstalkers manga (although Ultimate X-Men is quite mangaish sometimes).
I like the very first one. My dad has always referred to manga as colouring books, since he says he wouldn't be able to resist colouring them in if he owned them.
Though I think the pages would be better, more impressive, and more interesting if there was more than just a few colours. You should try colouring a nintendo 4koma. I have some Kirby ones I could supply you with if you want. I scanned them for the Rainbow Resort site. Some of my Dream Land 3 manga has been translated! It's weird though, since the Kirby 4koma actually tend to have a fair amount of sexual humour (specifically Kirby super star with the mouth to mouth feeding.) There was even one where Kirby said he wanted to see Adeline (from Kirby 64) in a bikini, and one where Kirby was depicted with 6 breasts. (that scan became a meme on the Kirby forum) There was also one where Dedede dressed in revealing women's clothing. (granted, it was an imaginary thought of a Queen Dedede.)
I wouldn't send any of those ones since they are weird, and some were already in Colour.
I also have some Golden Sun 4koma scans I scanned, but they aren't as good quality as the Kirby ones. Though brace yourself about posting scans, since even though they are edited, they aren't mostly your work. So they will probably be noticed at one point, and be removed by the evil deviantart staff.