In terms of information (concise, lay information at that!), this documentary was spot on. I found it on my DVR from the Discovery Science Channel (I routinely record "space" night every week). Though the film tends to focus on all of Robert Zubrin's theories exclusively, it's a great poster tool for pushing the agenda of manned space exploration past the moon. I suspect the film's title is a reference to the Mars society, and not to Mars geology (which is what I was thinking at first). Although I'm not a member of the Mars society, but I do agree with the case for Mars in general, and this was more exciting than an hour of watching the Mars rovers slowly dig an inch into Mars' surface.
Although I like to consider myself pretty familiar with these topics, this documentary really gave me insight into the history and primary concepts of the argument for Mars that I never really knew before. The Mars Underground actually answered many questions that I knew to ask from my experience that I would have thought would go unanswered in this short documentary. In the first few moments, I was already asking about radiation, provisions, bone mass loss (due to gravity), and the overwhelming cost of a short Mars trip only to throw around some dirt and plant a flag.
Dr. Zubrin's very bold plans really throw standard convention and the tendency to inject too much bureaucracy into a simple project. His almost shoestring budget and nearly arrogant propositions are aligned with the same thinking of the Apollo missions, Christopher Columbus, and other major pioneering ventures. But it's what is needed to take that next step and step out of our reductionist couch comfort to do what's right for humanity in the name of life itself.