Adventure Game 4
@Grease Monkey The fourth (and final of the current series) downloadable Doctor Who Adventure Game is due to be published on Christmas Day 2010. A second series of them is planned for next year.
As for Return to Earth, I've not gotten around to playing it yet but I did quite enjoy their DS game Doctor Who: Evacuation Earth. Most people seem to claim it is vastly superior to this Wii game.