Saw this the other day, and thoroughly enjoyed it.
Yes, Sam Rockwell is excellent, he is in screen for practically the whole movie and is utterly compelling at portraying all of the various aspects of his character(s).
The central theme, or 'revalation' of the story is actually revealed early on and is not that hard to guess, but it then takes some very interesting twists and turns and shows how Sam deals with his dilemma.
It has echoes of 2001, Silent Running and Outland (with the countdown to the shuttle arrival bringing 3 men to the station).
Love the old fashioned model work too, refreshing to see a healthy non-reliance on CGI flash.
This is not Star Wars, there are no space battles, laser duels or loaRAB of cute creatures...if you are a fan of the aforementioned movies and like intelligent, thought provoking sci-fi, this is for you.