Firstly, while Sam Rockwell's performance is fantastic, this isn't the type of role I most like him in. I like him in roles where I couldn't imagine anyone else playing the part. This one did not come across that way to me. I had the same sort of problem with Kevin Spacey's voice work. While it was pleasant to know it was him and hear that familiar tone, it really could've been anyone and it wouldn't have made a lick of difference to the film.
As for the concept of the story, I liked it without loving it as much as I should've. I liked it in theory, but not so much in execution. I thought it could've been crafted better, both in terms of the reveal to the audience and also how the concept was played out after we find out what is happening. The whole thing ended up coming across a little dull and boring for my liking and the final third of the film just kind of petered out rather than ramping things up.
'Moon' is a very good looking film though, there is no question about that. Add in a fine performance from Rockwell and a thought-provoking concept that will certainly intrigue most who watch it to some extent, and you have yourself a very watchable film. Just not one that I will likely be recommending to people.