You probably know that Nanook of the North is a documentary about Eskimos. But did you also know that it was the first "documentary," period? You did? Well, let's chuck a harpoon at a walrus and investigate anyway.
The praise: It hardly mattered whether or not Nanook of the North was good -- it was the first feature-length documentary! Isn't that enough? Nonetheless, when the U.S. Library of Congress began preserving "culturally, historically, or aesthetically significant" movies in a National Film Registry, in 1989, Nanook of the North was among the first subjects to be chosen.
The context: If we understand a "documentary" to be a movie depicting actual people and events as opposed to actors performing a script, then most of the first movies ever made were documentaries. The films of the 1890s got by on novelty alone -- the pictures are moving! -- and were nothing more than what we would now consider mundane footage: workers leaving a factory at closing time, a train arriving at a station, people bustling along a sidewalk, etc. When movies started telling narrative stories (The Great Train Robbery  is considered the first), the ones that didn't came to be called "actualities."
Then came the travelogues ("scenics"), popular in the first couple decades of the 20th century, which gave audiences the opportunity to see parts of the world that had previously been available to them only as photographs, if at all. Though these were undoubtedly very interesting, their focus was on the places and people, not on arranging them into stories.
It was Robert J. Flaherty (1884-1951) who first combined actualities, scenics, and storytelling. An explorer and prospector by profession, Flaherty came into filmmaking merely as a way of documenting the exotic people he encountered. He spent much of the 1910s among the Inuit people in northern Canada, working for a railway company, and returned with a ton of footage that he disliked as soon as he watched it. "It was utterly inept, simply a scene of this or that, no relation, no thread of story or continuity whatever," he later wrote.
But wait, wasn't that how most actualities and scenics were at that time? Yes -- but Flaherty had shot this footage himself and had lived in the "exotic" places it depicted. For him, it was no longer enough for a movie like this to merely show some other part of the world. He wanted there to be a story. Thus motivated, he vowed to return to Canada and make a real movie this time. (It undoubtedly helped that this first footage accidentally caught fire during the editing process and was destroyed.)
Sponsored by French fur trading company Revillon Freres, Flaherty headed to Hudson Bay again in 1920 and spent a year making what would become Nanook of the North. He looked for the right types to represent Eskimos in his movie, the way a casting director would search for actors. He convinced his Eskimo participants, who had started using guns and wearing European-inspired clothing in recent years, to revert to more primitive weapons and fashions for the sake of the movie. Some events were staged, though all reflected the actual experiences of the people.
Bear in mind, there were no "rules" about how to make a documentary of this nature. The word "documentary" didn't even exist yet as a movie-related noun. Nanook of the North was the first such film of its size and scope. We would consider some of Flaherty's tactics dishonest today, and documentary filmmakers are called out all the time for violating the established conventions, but Flaherty had no such guidelines. For the most part, he had good intentions. It hadn't been very long since the Eskimos had started using guns instead of spears and harpoons, for example, and Flaherty wanted to capture that former way of life on film before it disappeared forever.
It is also worth noting, in Flaherty's defense, that filmmaking equipment in 1920 was heavy and unwieldy. You couldn't just grab a camera and run around gathering footage, guerrilla-style. A certain degree of staging was necessary to film anything, let alone something in an icy, barren wasteland. If Flaherty had followed the modern rules of documentary filmmaking, the vast majority of Nanook of the North would have been literally impossible to capture.
Modern documentaries are seldom blockbusters today, but Nanook of the North was. Flaherty hadn't made it as an educational tool or to serve a niche, the way many docs are made today -- he'd made it with general audiences in mind. (It was released in 1922; general audiences were the only kind of movie audiences there were.) The fellow called Nanook in the movie (his real name was Allakariallak) became internationally famous, to the extent that when he died a few years later, his obituary ran in newspapers worldwide.
The movie: Meet Nanook. He lives with his wife and children near Hudson Bay in Quebec. He builds igloos for shelter and hunts seals and walruses for food. He smiles a lot and seems like a nice guy.
What it influenced: For one thing, movies like this are called documentaries now. Credit for coining the term goes to Scottish filmmaker and critic John Grierson, who used it in a review of a subsequent Flaherty film, Moana (1926). I'm looking at a film history book from 1939, Lewis Jacobs' The Rise of the American Film, and I note with amusement that the author puts the word "documentary" in quotation marks whenever he uses it. The form was still very new.
The Nanook effect was immediate. As Jacobs wrote in 1939, "Nanook of the North not only changed Robert Flaherty's future but added a new province to the domain of motion pictures. With his film was launched what was later to be known as the 'documentary' form.... It had no plot in the dramatic sense, nor was it fictional in the literary sense. The sensitivity of its director and his selection and arrangement of material made the film utterly different from and superior to the old-time travelogues."
Flaherty was immediately hired by Paramount Pictures to make something akin to Nanook. This time, Flaherty chose to visit Samoa, where he lived for a year and a half and came back with Moana (a Polynesian word for "ocean"). He subsequently made Man of Aran (1934) on the islands near Ireland and Louisiana Story (1948) in the American South. (The latter was completely fictional, though it's often lumped in with Flaherty's documentaries and is aesthetically similar to them.)
What to look for: Regardless of which specific events were staged, the film stands as a fascinating look at a real culture that actually existed. Pretty much anything shot 90 years ago would be intriguing today, even if it just showed everyday city-dwelling Americans. Nanook of the North shows a people who were far-removed from "normal" life even then, and only more so now. Building an igloo, harpooning a walrus, skinning a seal -- that stuff is mesmerizing.
What's the big deal: Surely it was only a matter of time before the genre of straightforward travelogues evolved into something more sophisticated, telling stories and depicting people's lives. Flaherty probably was not even the first person to do it. But he was definitely the first to do it successfully, and Nanook of the North introduced a kind of filmmaking that changed the medium forever. It's like cinema was a language and Flaherty invented adverbs.
Further reading: Flaherty wrote a behind-the-scenes article for The World's Work, digitized here. (Scroll down to page 632 for another Flaherty article, "Life Among the Eskimos.")
For historical purposes, you might also enjoy The New York Times' review from 1922: "The spectator watches Nanook as a man engaged in a real life-and-death struggle. And how much more thrilling the sight is than that of a 'battle' between two well-paid actors firing blank cartridges at each other!"