His style was meant to evoke tapestry art, in high fairy tale tradition. He played geometric and organic forms against each other and used solid areas of color. I felt this would be a suitable visual target for the computer graphics of the time. (A little history - I first started Sinister in 1999, so graphic capabilities were primitive by today's standards, and I was searching for a look that was achievable without compromise.)
One thing Eyvind discovered was that complexity can be visually inferred by starting with a dark mass and building toward lighter values with successive layers of pattern.
Even with today's computer graphic capabilities, there is a lesson here about economy and process approach for environment artists who deal daily with complexity issues, especially when depicting foliage and other organic forms. I decided the abstract look of Sinister would be one of simple layering of repeated patterns. I would start with a dark base - representing the inner shadowed core - and around that build one or two more layers of successively brighter elements, representing the outer illuminated layers. The benefit of this approach: you can handle the dark inner layers in very low resolution, saving the processing cost of higher-res elements for the outer shell where detail will be noticed. Here's a simple example based on Sinister's "target tree" - the tree he uses for target practice.
First, I build a lowpoly mesh in Maya by extruding polygons. I usually block things out according to storyboards frames such as those above, and then export individual meshes to their own referenced files. Here's the base mesh for the target tree in Maya:
Next I export this in .obj format to ZBrush, where I first build up the trunk.
With the fiber subtool selected, go to Tool>UV Map and click FiberUV with map size 256 or 512. Under Texture Map click New from Polypaint.
Hit GoZ and send this inner canopy to Maya. Save it out as a .ma file and close Maya.
After you've got all this assembled by importing trunk, inner, and outer canopy into a composite Maya scene, you should be able to do a Mental Ray render that looks pretty similar to your ZBrush master file. The poly count is reasonable, and provides good interaction.
Now, if you want to do something fancier, you can model any leaf-shape as a separate piece of geometry. Then instance it to all of your Fibermesh fibers. Custom leaf shapes! Geometry>Modify Topology>Micromesh>select mesh to use as leaves. BPR will render each fiber as the Micromesh (custom leaf) shape. To create permanent geometry out of the Micromesh (to export to Maya, for example), Geometry>Convert BPR to Geo.