Great composition, here! I have somme suggestions, throught...
First, your space ship's edge ar really too sharp... Actually, I was thinking it was done by computer. I know that using masks can be verry attractive, but if you do, you really should use it everywhere. This is why I usually don't use it! Lol! (I mean, if you look your hight light, there is one sharp edge and, except this edge, everything is blurry... It looks kind of weird... :-S)
I also see a little problem with the shades... I pass throught your gallery and I guest you're a Drew Struzan's fan, do you? Well, some time ago he started saling a DVD and I bought it. One of the first thing he said is to alway start on a gray board. It will allow you to blend your color far more easily and it will make your colored pencil a lot more visible. (He was right, I tried it and it works well!) Actually, I look the contrast between your characters and I'm pretty sure you worked on a white pannel or a verry light shade of gray.
Also, for the choice of color. I see a little problem with the choice of color : You worked with transparent yellow and blue wich will make a greenish color. I'm not sure but I don't think it is what you whanted! It is alway totchy to blend yellow with blue witout making a green result but the best would be to use an opact pigment.
Finally, the metal is alway hard to render. For the sword, I suggest you to use a darker pencill (8B, a black prisma color HQ) or, even better, black gesso. (Some people use black paint or black ink, but I think it ruine the board texture.
Something else I forgot. Do you use Gesso on your work? If not try it. Seriously, it helps a lot. It makes the surface of your board more receptive to some kind of pigments and it allows you to earase some parts (By painging Gesson over it wich wil be the same color as your backgroung). You can use the 50% gray gesso or using your own blend of white and black gesso depending of what you whant. Personally, I like adding some achrilic paint to it to get a little color totch!
So, I hope it'll help you and if you have any question, just ask!