I took Pierre Benjamin's Zbrush workshop 18 months ago and loved it. If you are looking to learn the techniques he uses in his great work, I highly recommend taking his course. Here are a couple of pieces I created during the course, based on an illustration by the amazing Wael Safwat. The second portrait is based on a 2D drawing by the fabulous Sebastian Krueger. You can check out their work at the following links. Their work will blow you away!