I ended up seeing this last night. I have to say it was well worth the trip.
It's been quite a long time since we've had a really good story driven sci-fi movie, and this one delivered perfectly. I can't imagine anyone other then Sam Rockwell in the role, the musical score was great, and Duncan Jones really put together a tremendous story. While the VFX were somewhat poor, the great thing about them was that it didn't detract from the movie at all. I felt like I was watching an old sci-fi movie and had no need for the slick CGI found in today's films.
A poster above said it was a little slow, but that really was the nature of the movie. It was all about discovery, and I thought the pacing was just about perfect.
Had this movie been made in the 70's (and it has the look for it), it would have been an instant classic that we'd still be talking about today.
I have to give it a solid 9.5/10.
I highly recommend you go see it if it's playing around you (and make sure you AVOID the spoilers!!!).