Now before you read this post, be aware that as compared to...pretty much everyone on here, I suck at pixelart. Like...your creepy cousin with a blindfold holding the gun backwards as compared to your trained sharp-shooter abilities.
Excuse the weird analogy there...
BUT I like to think I'm pretty weary when it comes to anatomy and Silent Hill. Since i loved Pyramid Head so very much I couldn't resist a quick c&c.

First of all, I don't think the lightsource should be head-on. Why? It looks too copy+paste to me, but this is mostly just my personal preference. If you really want a challenge and some way to capture the awesomeness of Pyramid head, try a lightsource from below or behind. But again; just my personal preference as a Pyramid head fan.

Second, the helmet should should be higher. Pyramid head doesn't ram people with his head; he stands tall and proud. While yours does look pretty awesome, it also makes the helmet look more like something superimposed over him rather than a "pyramid head." When you're drawing it, think of standing with your chin up and looking down. Now I realize this is a rather odd angle to draw, particularly considering the perspective you have chosen as a head-on pyramid-head-dude. I'm really hoping what I'm saying is making sense, by the way. I usually don't critique.

I really feel like I should nitpick that that there helmet needs to be a bit higher up though; I really cannot stress enough the need for a good reference, or even several considering how unusual this really is and since there is such an abundancy of Pyramid head pics on the web. Helm's picture depicts this quite nicely I believe.

Either that OR make it longer. With this perspective, I'd suggest sacrificing really being what Pyramid head was (I was going to have a picture here, but the only pic that satisfied me was too gory I think and I'm still new to this site so...not entirely certain wha'ts acceptable...anywaaay) for something that looks truly violent and "real" in this POV.

To define his muscles, I'd suggest lowering the contrast. For one thing that there blazing sunset you've got going on is rather hard on the eyes; it made me dim my screen so I could critique it. Although, that's another personal preference thing. But look again at Helm's picture. The colors and shapes flow very smoothly. Really, looking at your first picture, I feel like you could greatly improve on it just by regaining some of that--minus the overbearingly almost cartoonish muscle mass. Try to find a happy midway between the first and second picture. Honestly, though, the second picture almost does it for me--minus the helmet problems I nitpicked and stressed over earlier. When you look at Pyramid head, he is not a freakishly muscular dude. By which I mean, he probably wasn't a body builder. He was more like a butcher or a miner.

And for your picture, considering this is Pyramid head we're talking about, perhaps try incorporating something bloody in there.  I really wouldn't use the colors of a sunset on him; it's much too pretty.  Especially on his pyramid. But maybe it fits where you're aiming to use it. Obviously I can't really tell exactly what you're going for since I'm not inside your head.

I hope this helped, and I hope none of this offended you. I really never feel comfortable critiquing people since I'm not all that talented at anatomy or pixeling, or art in general. But still... Good luck!