
I loved this movie. LOVED
Acting was phenomenal, directing was outstanding & editing/sound were unbelievable.
This isn't in my top 10 or top 20 movies of all time, mostly due to re-watchability (hardly any), but it was without a doubt a spectacular film. Everyone should check this out when it's on DVD.
*SPOILER WARNING*
Basically Sam Rockwell is on a 3-year mission, stuck on the moon. He's taking care of 4 lunar collector machines that harvest and periodically rocket back to Earth supplies of helium-3, from the surface of the moon. It is a solo-manned station, with the exception of his HAL-like robotic couterpart, known as GERTY (voiced by Kevin Spacey) and he takes care of all the problems and the transportation of the harvester energy back to Earth.
There is no real-time link between Sam (both character name & actor) and Earth, so his only direct real-time interaction is with GERTY, the intelligent computer whose function is to attend to his day to day needs. With such little human contact and all of it indirect, he feels that three years is far too long to be so isolated; he knows he is beginning to hallucinate as the end of his three years approaches.

All he wants is to return to Earth to be with his wife Tess and their infant daughter Eve, who was born just prior to his leaving for this job. With two weeks to go, he gets into an accident at one of the mechanical harvesters and is rendered unconscious.
Injured, he awakens back at the station in the infirmary. GERTY tells him that a rescue team named Eliza will come to the station to clean up the aftermath of the accident. After his recuperation, he takes an unauthorized trip back to the broken harvester, where he makes an unexpected discovery; he finds his own body, still alive, inside the transport vehicle.
Because of his find, he begins to doubt his sanity, then his true identity, then the company and GERTY's willingness to do what is best for him. Because of his resulting beliefs, his sole mission becomes how to get back to Earth on his own.

Eventually Sam finds that he is a clone, and so is his other self. He has been cloned several times before, and millions of times thereafter. He can never return home, and each clone will die after 3 years, and a new clone is spawned to replace him. He is in a perpetual confined work environment, and is forever doomed to repeat himself.
A-