nicely done!
I REALLY like the pink haired one and would like to see that as a chara set. I think you have spriting hair down pact, the clothes on the left one are done well, I think, and the pants on the middle one I like, but the shirt on the guy and the far right ones I dont like. It may just be because its all black and my eyes aren't working right. Actually, now that I look at it closely, there is detail in the guy shirt.
Maybe you could throw a logo on it to add detail to his goth look. Maybe something white to throw in some contrast.
Im not sure what it is, but the one on the right is just not doing it for me. the hair is extremely well done (I can never find the right color for blonde hair...) I think the belt could use alittle more detail on the blonde.
other than that, maybe color there eyes to give life to them.
I like it, and look forward to seeing more of your work in times to come!
-edit-
maybe take the blue on the pants down a few notches, dont think I have ever seen blue jeans that blue
and add shadows to her thighes right underneath the shorts