Nice...
Good attention to detail, like how you got the patterns in the visor.
But...
When working with pencil, you might not want to just use a 5h. You should have at least gone over the major lines with something heavier (3-6B?) and then perhaps used a chunkier pencil to smooth the black spots. When you use an H pencil, as far as I can tell, the points tend to dig into the paper, creating usually undesirable ridges in the [paper that make smooth blending really hard. They make sharp lines.
B pencils are nicer for shading, but if you don't have any, that's totally understandable. <3
All I really have to say, in the end, is that you could have darkened the major lines and, well really, all the lines, so the details are easier to see. If you made the lines darker, that would also give you more chance to add extra details; like dirt or little scratches.
We all know you can't be as awesome as Master Chief without getting a few nicks and dings.
Overall, this is better than I could do with just one pencil. xD