It is free to use by downloading it from the Autodesk website.
It opens 3D DWF files.
Its graphics are considerably better then Design Review 2009.
It has a gravity tool that allows you go up and down ramps and stairs.
If you want to get an idea of scale you can use the Third Person Avatar.
Its navigation is a bit different, but it’s worth getting to know it. Considering it is the coordination tool for the next few years, it’s worth getting to know it.