Roger Ebert was undoubtedly the most influential movie critic of the modern era—not because he developed a specific theory of filmmaking that was widely embraced (both Truffaut and Sarris, in their advocacy of the auteur theory, were more important), or because he represented a highly personal way of looking at and writing about films that appealed to the intelligentsia (as Pauline Kael did), but because he wrote seriously about film in a breezy fashion that appealed to the masses and, along with Gene Siskel, popularized that kind of criticism on television. His reach, which also included books and latterly a major online presence, made him the most familiar, and probably the most trusted, movie reviewer around. He was also the first film critic to win a Pulitzer Prize, and to receive a star on the Hollywood Walk of Fame.

By itself, however, that probably wouldn’t have justified a full-fledged documentary about Ebert. It was how he lived out his last years—when thyroid cancer required surgery that ultimately resulted in the removal of his lower jaw and made it impossible for him to speak, eat or drink, and yet he continued to work indefatigably—that made him a heroic example of what might be called, in the hackneyed phrase, the indomitability of the human spirit, and undoubtedly convinced Steve James to make him the subject of a feature-length film. James, of course, had ties with Ebert. He’s a fellow Chicagoan (Ebert, though originally from Urbana, where he attended the University of Illinois, was based for most of his professional life at the Chicago Sun-Times). And Ebert championed James’s debut feature “Hoop Dreams.”

The result is generally an admiring, and admirable, portrait of Ebert as a writer and as a person. Using archival material, excerpts from his memoir read in voiceover by Stephen Stanton, and comments by newspaper colleagues, friends, filmmakers like Martin Scorsese, Errol Morris and Werner Herzog (along with young directors whose work Ebert happily promoted) as well as fellow critics, it ably covers his childhood, his early interest in journalism, his years at U of I (where he was editor of the Daily Illini and wrote some stinging editorials), and his work at the Sun-Times. It also gives substantial time to his collaboration with Gene Siskel on the film review program they began at PBS (under the title “Sneak Previews”) and went on to syndicate until Siskel’s untimely death, using clips from rehearsals as well as finished episodes to illustrate how well they worked together onscreen and how acerbically they treated each other off. It goes on to consider his growing celebrity as lecturer and talk-show guest and finally his late-in-life marriage (shown via home movies, among other sources), before turning to the serious health programs that struck in 2005.

Ebert gave James unprecedented access in the last months of his life, allowing him to record the painful process by which nurses drained the phlegm from his throat and his sessions of physical therapy, as well as the time he spent with his family and devoted to watching movies, writing reviews, and directing the development of his website. What emerges in this footage, interviews with his wife Chaz, and responses that Ebert typed in response to questions posed by the director is how active and dynamic Ebert’s mind and will remained even as his body was reduced to the merest shadow of its former self. When he finally decides that the pain has become unbearable and decides to let go, you actually feel that you’re losing a friend, so engaging a portrait has James used the varied material to create.

But that doesn’t mean “Life Itself” is simple hagiography. Though James certainly presents a deeply felt and laudatory view of Ebert, his film doesn’t overlook more problematic aspects of his life. The alcoholism he developed during his early newspaper days gets substantial treatment, and Chaz reveals that they actually met at an AA session. The rivalry between him and Siskel is well caught, and it’s clear that especially in the early days the two men disliked one another. Even in the footage from the final months, James takes pains to include moments in which Ebert gets frustrated and takes out his annoyance on his wife and his caregivers.

The overwhelming image one gets, however, is of a man of incredible literary facility who loved films passionately and was able to express his judgments of them with enthusiasm, an incredible breadth of cinema history and clear-headed discernment. Time Magazine critic Richard Corliss once wrote an article lambasting what Siskel and Ebert were presenting on their show, with its “thumbs up, thumbs down” decisions, as a cursory approach that demeaned real film criticism. But looking back he now admits that their capsules were uncommonly perceptive and substantive despite their brevity; and going back to Ebert’s published reviews, it’s hard not to agree with Kael’s observation that he was penning the best newspaper film criticism of the time. (She, of course, was writing longer pieces for The New Yorker at the time.) Even in his later years, when his opinions grew steadily more lenient, Ebert’s writing remained fresh and nuanced.

“Life Itself” is a generous film, but also one that’s been carefully assembled by James, cinematographer Dana Kupper and editor David E. Simpson (with an assist from James) to present a comprehensive view of Ebert that’s not merely touching but honest.