Another thing you need to work on is anatomy.
I don't mean correct proportions, but their limbs and such should all be the same length and everything ( note how that is not the case with the.. boxer..? in the first post ).
Also, your characters need some better proportions to be more flexible. You almost always draw them with their hands down, and I can't really imagine them being in a different position, like cheering, hands pointing up.
Also, look at the soldier with the shotgun. Thanks to his lack of fingers, he isn't actually holding the gun, he's kind of balancing it on his hand, and the right hand ( from his view ) seems to either be one half too short or to bend wrong.
A different, cartoony style is nice and all, but it has to actually work, too.

..also, I wonder whether you ever drew a woman.