I like the fact that a freeware can actually throw you back great renders and visualizations as good as the ones you can get in +1K softwares. I also like it's compatibility, even though it's a bit limited you can use other free softwares like SketchUp or blender as a "bridge" to get really nice renders. When I was an active Kerkythea user I used to export my models from rhinos to blender and then to Kerkythea.
I like how realistic it can make a Sketchup View look. Between the varying levels of light and surface reflectivity, and the different materials you can add, you can really balance shade and shadow and light.