I won't claim I'm an expert or anything, but I'm always willing to help if I can!
So, I know this is probably too late, but here's an image you could use for reference (in cleaning up this model, or for future models):
It's a nice layout of great topology for a head, could really help out in visualizing how you want to lay your own polies down.
I think your topology overall is almost there, you really just need to tweak a bit more. Like Illusions pointed out, I think you need to start pulling your verts out to indicate the muscle and fat more. Right now the face looks like the skin is stretched across the skull-- space it out more to show that it's not saran-wrapped around the bones! [img]/images/graemlins/wink.gif[/img]
Plus, the muscles down the side of the neck (Sternocleidomastoid) goes from under the ear down to that center notch at the base of the throat/top of the chest. Right now, yours is starting from under the jaw. Move that back to the ear and the model will look way better. I think the neck's definition is fine, even for a base mesh (you can always tweak verts a little to suit later needs).
As for the legs, they are too straight up & down. From the front, they should look they sort of curve from the outer hip to the inner knee. Topology should always follow muscle AND bone structure, in my opinion, regardless of the output (game, film, whatever). But that's just my opinion, take it as you like [img]/images/graemlins/smile.gif[/img].
From the side, the legs should curve back from the front of the hips to the back of the knee, then almost straight down from knee to ankle. I did a quick paintover on Dabu's Asian Goth Girl, take a look at that to see what I mean:
The same method applies, it's only more exaggerated in women than in men. Looking at the side, I'd say bring the pelvis forward a little (so the abs look a little more up & down), and the knee back, so the arch of the foot is straight down from the ear. The arch is ALWAYS directly under the mid-section of the head-- that's where a bipedal's weight is planted, for optimal balance.
Damn I wrote a lot. I hope this helped-- it's all suggestion, so take what you need from it. You're on the right track, in my opinion, so keep it up!