The concept is cool, and your composition is great, but you need to work on your line-art and shading... You need to show depth in the background, it would have really made the image pop more. Warhammer 40K has amazing artwork so you're influences are great, but along with all the cool stuff, I'd recommend doing some anatomy studies, and looking at some fine art to get a deeper understanding of lighting and depth. Keep at it, though, you're on the right track!