Snowden explains how "metadata gathering" works pretty clearly. At on point he left me wondering of the NSA could snoop on cloud backups -- of computer files never sent or published anywhere. Just yesterday, Carbonite on one of my computers suddenly got itself uninstalled. It sent me a chilling thought half way through the movie.
I don't usually give star-count ratings, but this one deserves five stars if any film does.
Update: Nov. 23, 2014
I've reviewed Glenn Greenwald's book "No Place to Hide" on my Book Reviews blog Nov. 22, 2014. There's a lot of material on "what journalism is" as well as a detailed account of the 10-day meeting with Edward Snowden in the Mira Hotel in Hong Kong.