Sure, it's a propaganda film. But that doesn't make it any less a classic piece of art. Art is about form more than content. Two of the most classic films of all time -- Birth of a Nation and Triumph of the Will -- deserve a 10/10 rating for their form, but their content is worse than reprehensible.
Just as DW Griffith was embarrassed by the criticism he received for Birth of a Nation, Disney must have been similarly embarrassed at the reaction it received for Our Friend the Atom. A few years later, they produced an updated (and greatly shortened) version called The Atom: a Closer Look, where they point out some of the dangers of nuclear power that they omitted in their first film. Both Disney films can easily be found on the Internet for free, and are certainly worth a look.
As you can see from the reviews here, nuclear power is a controversial issue. In fact, it's such a controversial issue that it's much easier to find people who completely love it or people who completely hate it. Balanced views are few and far between -- the only balanced view I've seen is the short and informative Wikipedia article on background radiation.
I found out about the film via the anti-nuclear book "The Radioactive Boy Scout." The author mocks the movie as rah-rah propaganda, which isn't far from the truth. Still, nuclear power is becoming a more important issue than ever before, thanks to the impending catastrophe of climate change which we must quickly solve somehow. Therefore, it is important to consider all sides of the argument -- both pro-nuclear and anti-nuclear. You can't hope to learn the truth if you've only seen one side of the story.