Oh wow. I want to say that your ability is awesome (for lack of a better word because of my poor vocabulary).
I really like the hi-C(?) one in particular. The realism ones are particularly nice because of the shading you've employed. There's the certain texture and pressure to it that just makes it pop out.
I would suggest maybe trying to exaggerate the shading a bit more - contrast in lights and dark to make it just jump out a bit more. That's all I can say there, because it seems you have a very good eye for following lines and getting shading down from there.
On the very first one you posted, there's something odd about the shape of the body. It seems rather stick-board figure, unless the person is like that. Otherwise, perhaps look at anatomy a bit more carefully to get the very slight curves of the torso to flow. Or maybe it's the shading that makes his torso look a bit like a cylinder. Though it may be just me.
Your fanart is nice, very accurate in line. Though, maybe you should stray away somewhat from that now. Try your own things and find your own style. You know, just experiment here and there.