If you haven't seen what it does before, there is a set of videos at this link:
Revit Landscape - Urban Design: Lumion 3D
If you want to see a project go from Revit to Lumion (also this thread):
A free version for non-commercial use is available from this page. The free version will apparently be updated to version 2 in January 2012 (only a few days of that month to go...)
The company line:
Lumion® is a real-time 3D visualization tool for architects, urban planners and designers.
It’s perfectly suited for creating videos, still renderings and live demonstrations with a quick turnaround.
Lumion offers excellent graphics in combination with a fast and efficient workflow, saving you time, effort and money.
It is in fact so easy to create awesome still renderings and videos with Lumion® that it almost feels like cheating.