well I think you just need a little more contrast with your shades tbh, if you're going to stick to more of a cell shaded look you can afford to make the best of what you've set out for yourself.
You've got a lightsource here so why isn't there any shadow underneath the head? where the neck is visible should be noticably darker since not as much light can hit there. You need to visualise this everywhere, It's just a case of trial and error, work on this section by section and try to think where the light would hit least to where it would be hit most.
But in all honesty your latest is a great improvement, I think it just needs some warmer tones in there cus its all a bit too yellow. Just pushing the darker shades over a smidge closer to a warm brown. Reminds me of mustard atm.
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I made another edit of my edit too btw, may help. It's a choice to interprate light and dark into the lines too, not for line thickness value but to further act to shape. Just think, would a line be jet black if its the edge of the side facing the lightsource directly?
http://img179.imageshack.us/img179/5999/pokemonbr1.pngpokemon sprites do this, and along the same track with using limited colours.