Nice job man, I have to say, for your first attempt it looks good. I love the weathering. Like it was pointed out earlier, it may not be screen accurate, but it definately shows you have the most important aspect down: This helmet took a beating.
Also, I was able to put my finger on why it appears Manga-ish.
The front area at the mandibles is stocky and not as long as most of the other helmets. Almost like it's been squished.
I like it.