I would like to see more sharpness, at least up front. The lens is a great lens, but getting any DOF requires a aperture more forgiving that f4, even with a tripod. I would try some different settings....move up to f16 or somewhere in that area.
I would also like to see some background color, which would add some context to the subject.
Shooting macro is fun, and the more you shoot the better you get. Using flash can also get you those tough shots where lighting is poor.....just try more DOF and shoot a lot! I prefer hand held shooting with SR, because a tripod set up limits the composition.....by the time you get set up, the subject is often gone.....but a tripod is no doubt better for some shots. Try some hand held with flash and see what you get?
Here is one where I had a shallow DOF, but enough to get the part I wanted in focus. I was using an old 645 120 Macro on my K20D, so stopped down to f16 or so gives you a dark screen and makes Macro very difficult...you don't have that problem, so you can pick this up pretty quickly.
Pentax User Photo Gallery - Alien Bug?
Best Regards!