I guess I'll comment one by one.
Sai- Hair is good, clothes is good. Background isn't that appealing to me. The shading on the skin makes him looks more feminine.
Deidei - Nice sky, but the brown stoney area ruins it. It needs more shading in my opinion. Hair is not too bad even though I do prefer to see more strands. More shadings on the cloak too.
Sasori- Nice hair, again. Same problem, shading on the cloak. I dont like the white lines too.

The chakra string, wonderful.
Naruto- I dont like the hair in this one. I dont really know what to do about it though because Naruto's hair had been a problem to me too. Once again, I like to see more and more shading on the clothes. Background are too dull. Add some more colours into it to make it look more interesting.
Neji- looks like anime-style to me. If that's the case, then the hair is a bit strange. Shadings on the clothes again. However, for anime-style, you dont have to smudge it or blur it.
Overall, they are good. Your main problem will be the shading on the clothings.