I like the shell on the sand, but the only thing that seems to bother my eyes is the fact that it's not completely in the center of the pic, so the blurred sand catches my eye more than the shell. I don't know if there's much you can do about that.
good lighting and tones, the softness bothers me some, keep in mind that macro lenses have very shallow depth of feild so a small apature is needed, it looks like it could use alittle more depth. over all good job!