I bought Moon two months ago to have something to play on the plane.  I was a fan of the play control, though it was a bit hand-crampy.  I also really liked the atmosphere.  It kind of reminded me of the citadel in HL2.  But I don't think it was that great of a game overall.  The level designs were a bit too linear and uninspired and the combat didn't really get good until near the end.  Here is a tip for anyone that wants to play: start on the Veteran difficulty setting.  It is much mroe interesting that way.  Anyway, I put it at like a 6.5.  Not horrible, but not great.  I do hope they do a sequel, though.