I'm not a fan of realism, as a cartoonist i've had a bias, but I will blatently comment with no such bias.
You have a certain skill is perceiving images smply as they are. With no concept of creation it would seem as if you drew the things infront of you, or just re-draw other people's work. This isn't art, as real art must be changed at least 40% just so you can own the art. So when it comes to originality, you don't have much on you.
Now as I am a "Lowly anime" anime artist, you may think me insane, but I have to say, when it comes to color you understand your light sources. Shape is somthing you also understand, the form of the girl in the Sin City poster is very good, and yet again it's light sourcing is nicly done.
You have the skills to be great, but I'd hope to see some original reditions of the world within you, not the world outside you. But you are an artist, draw what you feel is right.
but.... you lack originality it seems, because I mean, you seem to have three arts of real life celebs that seem to come straight from the posters itself. And the pose of the girl *your original character* seems to lack unoriginality and she looks rather generic.
Keep heading on. :)