This image was created using the 2.5d Pixol technology in Zbrush. All elements were created seperately using (not so) primitives and then masking and extruding individual parts and then placed onto the image in 3d space.
After the image is complete, I render several different passes (within Zbrush), such as shadow, specualar, color, etc. and then composite them together in Photoshop. I make use of the Z depth pass that Zbrush allows you to grab from it's canvas to add depth and fog effects, and to combine a few different color passes.
This image took me roughly two days to complete, but I am getting faster at placing objects onto the canvas, so in the future it will be easily faster to complete an image like this, especially because my library of completed primitives is growing.
The beauty of Zbrush and Pixols in general are that once a 3d object is placed onto the canvas, they become light as a feather memory wise, allowing you to fill the canvas with many millions of polygons with very little slow down. This particular image (if I was counting) would probably total 30+ million polygons. But, like I say, I don't have to count with this 2d/3d hybrid program...
Final render size 3200x4096 pixels, prints will be around 3 feet x 4 feet long.