If you're looking for a good, even-handed overview of the Rosenberg case, this isn't it, but it is nevertheless not without interest.
It's not a good overview for two reasons. First, the movie spends little time looking at the actual facts of the case, focusing instead mostly on the effects on the family left behind. This can be excused, since it wasn't the intent of the filmmaker to cover the case itself. Second, and less excusable, the movie seems essentially uninformed by much of the evidence that has come out in the last decade (e.g. from Soviet intelligence archives) which provides unambiguous answers as to what the Rosenbergs actually did.
For instance, you won't hear here that documents in the Soviet archives explicitly describe Ethel Rosenberg helping to recruit David Greenglass to pass on atomic bomb construction details from Los Alamos. Ethel may not have deserved the death penalty for what she did, but it's hard to put much weight on any opinions this movie expresses on the subject, given its reliance on the pro-Rosenberg side for its view of the case.
That one-sidedness, however, is what is responsible for one of the film's two real accomplishments: giving the viewer a clear view of the mind-set of the American left in the 30's and 40's, one in which spying for a foreign power for ideological reasons was not merely acceptable, but laudable, and one in which the bald-faced claims of the complete innocence of the Rosenbergs were credulously accepted. The interviews with the aging members of the American left alone are worth the time of a serious student of the era.
The other interesting aspect of the movie is its clear documentation of the havoc the Rosenbergs' wreaked on their family. As a number of reviewers have pointed out, this is not a polished film, but the lack of polish contributes to the effectiveness of this portrayal. The Rosenbergs' willingness to put their family through this is perhaps the best measure of the depth of their devotion to the socialist cause, and helps us understand how they could have helped pass some of their country's deepest secrets to a foreign power.