one way to improve this piece wold be breaking up the clean structure right now this is a perfect rock as all the sides and edges are unbroken. Rocks are often fracturing and and naught perfect. Zbrush is a great tool for doing this eg. live boolen, mallet brush, or subtractive dynamesh.
Hey dude! If this was a smaller rock, I think you should be putting more detail into the sculpt, and relying less on the material. Your material isn't too well constructed and doesn't look very much like your reference. However, from what I'm able to deduce, it looks like you're trying to create a large rock structure. I…