Took this with my first DSLR, Pentax K100D with the kit 18-55mm lens. I love this shot! I also just upgraded to a Canon 30D, and bunch of canon lenses (non-kit).
The top of his head being gone doesn't bother me in the least. It's got a nice tonal range, I'd try bumping up the whites a bit with curves.
That'd put the highlights in his hair a little higher on the tonal scale and lighten his skin tone a bit. Without that I think it comes out a hair flat.
Thanks for the tips! Yeah, I wish I wouldn't have cut the top of his head off... But it was one of those shots where it happens SO FAST, I got what I got.