Common Ground is about perceptions and misunderstandings: the player experiences a set of events from the perspective of three protagonists. Their respective ideas of what is going on (and why) dovetail together in sometimes-surprising ways, and the result is a story about communication and expectation in an ordinary family.
Because of the way it plays with overlapping experiences, Common Ground also has to keep track of what you've already done (in one incarnation) in order to re-present those actions from the perspective of later viewers. This concept is not exactly unique in interactive fiction -- see Sam Barlow's somewhat frustrating The City, or J. D. Clemens' time-travel puzzler Möbius -- but Common Ground handles the technical aspects smoothly and treats the gimmick less as a puzzle premise than as a literary device. The fact that you get to re-view your actions from the outside gives a little extra shading to the usual player/protagonist relationship, too: it helps to make the characters seem less like toys, more like real people.
Many of the techniques used here are necessarily unique to text. A realistic 3D render wouldn't be able to convey the inconsistencies in viewpoint, and even with stylized art it would be hard to get across all the nuances. Different characters, for instance, notice different objects in their surroundings, though the setting does not actually change from protagonist to protagonist. The phrasing of descriptions is important, too: Stephen Granade is fond of using diction to characterize the viewpoint character (see also his more recent Child's Play).
If I have a complaint to offer against Common Ground, it is that the game occasionally feels a bit too generic, the characters insufficiently sharp-edged and individual. But this is only true some of the time; and besides, part of the impact of the story has to do with the ordinariness and universality of the people involved, the slippages and cracks in (what was supposed to be) safe middle-American life.
N.B.: Common Ground was built using TADS, an interactive fiction engine created by Michael J. Roberts. To play the game you need to install a TADS interpreter on your machine, and download the game file. We link to TADS interpreters for Mac, Windows, and Linux above, but you may be able to find interpreters for other systems. Those new to interactive fiction may also be interested in the introduction found here.