Moon - a quirky film from the other side

I was loaned this DVD after answering yes to the question about whether I like sci-fi films - well I don't dislike them but then I am not a real fan - but maybe that is due to limited exposure... So I decided to get into this one, despite it being released over 3 years ago... Sam Rothwell, the only real actor played Sam Bell, an astronaut miner, who was extracting helium 3 from the dark side of the moon, to solve the earth's energy crisis. He lived alone on this futuristic moon base and was 2 weeks away from returning to earth at the end of his 3 year contract - at least that is what he thought, until he realised that the next astronaut had been thawed and was ready to start working - a super enthusiastic clone. So I was with the first Sam, assuming he was the real one and this new one was the first clone - but as he challenged Sam, we realised that perhaps Sam was also a clone - this was at first unnerving. But then it became clear that maybe human bodies only last 3 years in this hostile environment, psychologically and physically. Had the corporation, Lunar Industries, solved the human resource and safety issue by cloning enough 'people' to keep their mine going ad infinitum? The skype type of interface with his earth family may well have been a re-run of old tapes. The only other interaction he had was with the robot Gerty (voiced by Kevin Spacey) - and this was also confusing because while we expected total confirmity to the company mantra, there were hints of almost human understanding, at least before he rebooted Gerty as he walked away... And then I found out that the director and writer Duncan Jones is David Bowie's son - and that it had been made on a shoestring budget... Did he really overdose on Major Tom and Ziggy Stardust as a child?