Yes, I have used Shiva, I followed some tutorials and I rendered a couple scenes with my models. The editor is a bit differnt than others so I could understand it only with the help of a tutorial. But then it made a lot of sense to me. The scripting is LUA but I did not do a lot scripting there, so I cannot tell much about the API design.

Graphically Shiva is very good and it supports a lot of platforms even Linux among them. But since I also did not find occlusion culling, zones or portals I would use it for small projects on a phone as an example.