The overall piece looks flat, you shouldn't just shade each rock individualy, but think of them as a single mass
Take a look at this: 
http://i35.tinypic.com/15wiiqc.png
On the big rock, each small rock is shaded individually, but they are also shaded together as one big sphere
Wow These are good, I'll definitely use these to help me out. Thank you for the help!
I think the rocks on the tile set below might help you refine this a bit more.
http://www.spriters-resource.com/psx_ps2/alundra/navabeachnhuntingrange.png
Hue shifting? I've always been a poor colorist, but this certainly helps. A Lot Thank you very much!
The rock shapes are looking good, but I think you need to improve your colour selection. Firstly, reduce the saturation; secondly, increase the contrast and finally, try using some hue shifting. There was a recent discussion of this in the forum relating to hue shifting and I think you could benefit from reading this post by "God_is_evil".
Excellent point! I can't slack a little bit can I? haha