yo waddup, roi!
don't listen to snake because your mapping is fine. although, I advise using a 1024x512 template since its much easier to map and get certain details in.
even though it's hard, just try and try. I also started off 512x512 but after using 1024x512, I automatically switched to it.
about your head, mapping is fine but I'm 100% sure it'll be much better if you map it in a 1024x512. I really love the eyes and the skin shading/shadows. robot part has a nice design and glow to it. though, I feel weird about the top of the head though, looks like his forehead is the size of (insert something big here). maybe it's just me since I haven't seen a lot of bald textures.
overall, I really love your art (as always). keep improving man, I see a bright future ahead of you!
ps: just do 1024x512 ♥