If you can help me learn to properly diagnose my work I would be grateful.
You have got a great lens, Sam. It appears, however, that you don't use all its potential.
What Frank pointed out is a clue : some of your pics are slightly blurry. Just because you handheld you camera.
Your pics are good, but perfectible. That would be easy, just use a good and stable tripod, and you'll get razor-sharp images. That will allow you using longer exposure shots, but never forget : the tiniest breeze or draft will ruin your image (tripod or not), even more with large reproduction ratio.
Also, you could use a flash, but the images won't be as nice with natural light.
That said, you have already a very good habit : you take your macro/close-up shots in the shade (or diffused light) which produces the best lighting. The sun is my second enemy after the wind in macro-photography.