The question of whether Edward Snowden acted as a patriot or a traitor would seem to depend on the degree to which one regards the laws which allow surveillance of US citizens as constitutional. While employed as a subcontracted systems administrator by the National Security Agency in 2013, Snowden fled to Hong Kong with an unknown number of stolen NSA files and crossed a personal Rubicon by leaking roughly 10,000 carefully-chosen documents to the media.
Snowden's decision had been motivated by an overwhelming sense of revulsion at the all-encompassing extent of the NSA's surveillance, not only of putative "hard target" opponents, like Russia and China, but also its European allies, and most disturbing of all, US citizens.
To list some of the most egregious of the programs: "Bountiful Informant," a database of the phone records of millions of Americans, provided to the NSA by Verizon through a court-order; PRISM and "Upstream", which gave the agency unlimited access to millions of American internet accounts, with the full cooperation of companies such as Google. Apple, Microsoft, Facebook, and others; "X-Keyscore," a powerful analytical tool which allows panoptic surveillance of almost anyone in the world, including the highest government officials or corporate CEOs based on nothing more than their e-mail address.
These programs are merely the tip of the iceberg, but they suggest why the quasi-totalitarian nature of NSA's surveillance activities were disturbing to so many, not the least, unwitting allies.
Not long after his revelations became public, Snowden was charged on two counts of violating the Espionage Act of 1917 and one count of theft of government property. Given the myriad complexity of the legal aspects of his case, it is impossible to treat them with due measure here. However, in this context, it's worth noting that the Espionage Act of 1917 prohibits defendants from making the argument that their actions in the crimes for which they were charged were made in the public interest. This is the essential reason that Edward Snowden has not returned to the United States to stand trial.
In the history of the United States, only one person has ever successfully defied a law related to national security and not either been imprisoned or exiled. That person is Daniel Ellsburg, a major supporter of Snowden. As Mr. Ellsburg has said, for an American who has released "classified" information, the Espionage Act does not allow for a whistleblower defense. Therefore, as NSA director Michael Hayden has said, Snowden will likely die in Moscow.
So, in essence, Snowden has sacrificed his life in the United States to remind Americans to defend their Fourth Amendment Rights. Therefore, he is a patriot.