I went to the theater five times last summer and watched it. I loved it. My review is here.
The title refers to Harriet Tubman's Underground Railroad in the 19th century; Rev. Bryant contends that we need a "new Underground Railroad" to help lead blacks from the tyranny of enslavement by the United States government which is bent on keeping so many dependent on the government dole.
The documentary is a masterpiece of photography and symbolism as well as strong in its powerful message. Yet even with the seriousness of the subject, in the end I was left optimistic and hopeful.
I've ordered my copy already because even though I almost know it by heart by now, I still want to watch it over and over again.