Well the thing is, you sorta need to mash the shoulders into the face if you want to get the perspective right..
Although a lot of games tend to screw the perspective so it's up to personal preference I guess

haha thanks man i can't believe i never noticed that 

Haha, it was the first thing I noticed

I love these sprites, it's an awesome style and I wish I could make such sprites as well!
Clean, colorful and very unique features of each one. (although I see a re-occuring theme with glasses and goggles )

Surprised no one has commented. This has a sweet old school feel, it's hard for me to point out anything specific apart from the movie posters which are horribly blurred and doesn't fit the style.

I also see some places with smooth shading or lighting which looks kinda off. I'd try to stick to just pixels and dithering for lights to retain that old school feel.
And I think the dirt is a bit too detailed, fewer colors would make it look more consistent with the rest.

Ok, first off let me say that if you want to improve, you need to live and breath sprites. Look at other peoples sprites. Edit sprites. Try to copy other sprites. Just making stuff from scratch won't get you far unless you're an expert on human anatomy. And then there's also basic pixel art knowledge.

Someone linked me this tutorial a while back, and I've been reading it several times, and it's only now after a few months that I really understand most of the stuff.
http://www.pixeljoint.com/forum/forum_posts.asp?TID=11299

Now for this particular sprite:

- Lacks contrast
Needs heavier outline. More contrast between shading and highlights.

- Perspective
In a 3/4 perspective, you'll be seeing mostly the top of the head, and thus the shoulders should be closer to the head.

- Skin tones
Try to make the darker shades red and the highlights yellow. But don't overdo it.
Just using shades of brown makes it look strange.

- Jaw line
Looks kinda weird with the pixels placed like a L, try to avoid that.



I'm not that good at anatomy though, so my arms and legs might look strange. (I'm really bad with feet too)
I also tried to make him more square headed, but that's a personal preference I guess.

Edit: I should probably not have moved down the ears, because that messes with the perspective.

Edit: tweaked it further with improved perspective. (also removed mouth, personal preference for low res sprites)
I also thought the eyes were a bit too feminine on my edit, so I made a female version too with slimmer shoulders and no shorts

I had some time to kill, so I played around with this really quick.
It was just for fun, and to keep me from getting rusty so it's probably filled with errors