If you don't have plans to see this movie, you can check the spoilers here and then come back.
A slow start, but then this movie becomes very interesting very fast, then by the final act downright riveting. Mostly I'm impressed by what principal actor Sam Rockwell and director Duncan Jones as well as the crew were able to do with what they were given/had to work with. I've been a fan of Rockwell awhile now, but clearly this film is a next-level move for him as he's the only performer for nearly two hours and more significantly has to play off himself, a feat that no amount of technology can make easier. Rockwell defies expectations and excels, playing the range of emotions masterfully, deftly differentiating his two roles, providing some light comedy as well as heart-wrenching moments, handling difficult physicality and generally giving the story its arc; it's a pretty incredible feat. Similarly, Jones and his crew manage to recreate the freaking moon on what doesn't look to be a huge budget with an end effect in many ways more believable than any amount of CGI and also shoot the same actor interacting with himself both in conversation and even fight situations so well you don't even notice "the strings." I really had an appreciation for the music chosen (probably no surprise given that Jones is David Bowie's son) and the uncomfortably good makeup job done on the ailing version of Rockwell's character. And hey, Kevin Spacey has had quite the career, but the voice of a semi-sentient computer may well be the role he was born for. I wasn't so much blown away by Moon as deeply impressed; I don't think I'll be watching it again, but it held my attention quite well and I certainly came away with a deep appreciation for the work put in.