I like your overall concepts, but you need more work on lighting. For a lot of your portraits, your shadows are too hard. Another alienbee or 2 could've fixed that. And don't put the light directly in the face. Otherwise, the whole face is lit up and it lacks depth. Portraits generally look better the other way around IMO.
And turn the lighting way down too. A lot of them are overexposed and underexposed. Like the girl in the black shirt.. You can't tell where the shirt ends and the shadow begins, and vice versa. And the one with the girl sitting with her back to the tree and the guy squating on a rock in the background.. She is lit up like a Christmas tree on steroids but he's dull and lacks color.
Overall, pretty good work though.