Michael Barrier offers a guide to Disney live-action movies. It's pretty good, and while I disagree with him about Mary Poppins, I do agree with him that Disney's live-action movies suffered from his directors' tendency to treat them like television shows. Robert Stevenson was not, in fact, primarily a TV director, but he and other Disney directors tended to shoot everything like a TV episode of the era: relatively static camerawork, lots of back-and-forth cutting during dialogue scenes, and rather cramped compositions. Some of the numbers in Poppins would benefit from more fluid camerawork, a la Arthur Freed musicals (though in some cases the static camerawork was a product of necessity: the camera couldn't move much during the animated sequences or it would have made the animation prohibitively expensive to do). On the other hand, talking about the contributions of directors in the context of these films is a little pointless. Disney's live-action films were often as meticulously storyboarded as animated films; many of them were co-written by cartoonist Don DaGradi, who "wrote" his scenes in sketches, just as he would "write" the script of an animated cartoon. Whoever the director was -- Stevenson, Ken Annakin, or TV-based Norman Tokar -- his mission was to execute a visual plan that had already been worked out, not to create the visuals on his own.
The one person who did have a major, auteur-like role in Disney's live-action movies was writer-producer Bill Walsh. He wrote many of the Mickey Mouse comic books and comic strips -- in the '40s, the only place where Mickey was allowed to have an edge -- and when Disney started to branch out into live-action features, Walsh became his star writer; he wrote (usually in collaboration with DaGradi) The Absent-Minded Professor, The Shaggy Dog, That Darn Cat!, Mary Poppins and, after Walt's death, The Love Bug and Bedknobs and Broomsticks. His track record made him one of the most successful producers of the '60s, in box-office terms. His scripts represent what Walsh thought a live-action family comedy should be: wholesome fun, wacky, cartoonish special effects, and a generally positive attitude (without the dark moments found in some of Disney's '50s movies, like Darby O'Gill). "After 1960 all is darkness," Barrier writes about Disney's live-action ventures; what happened after 1960 is that Disney movies largely became Bill Walsh movies -- even Poppins, which Disney was certainly heavily involved with, is very Bill Walshian, with very broad jokes (the family scrambling to catch vases and such after the Admiral fires his cannon) and an overriding morality that's not entirely Disney's -- the film concludes that George Banks should stop working so hard and relax; "pure" Disney movies, like Pinocchio, tell the hero to stop relaxing and start working hard. What you think of Disney's post-1960 product is largely dictated by your appetite for Bill Walsh's sense of humor.
Of their kind, Walsh's films are extremely well-written and never insult the intelligence of the viewer; there's an art to writing dialogue that is simple enough for children to understand while sounding grown-up enough to please parents as well, and Walsh was good at it. I recall a post on a message board mentioning that one of Disney's veteran animators -- Ward Kimball, I think -- considered Walsh a genius on a level with Disney. That may be a bit much, but certainly the films Walsh wrote and produced in the early '70s are streets ahead of those produced by Disney's son-in-law Ron Miller, and the descent of the Disney studio into mediocrity and near-bankruptcy was hastened by Walsh's untimely death in 1975.
Here's a description of a script Walsh and DaGradi wrote that didn't get produced (because Disney died and no one else at the studio wanted to greenlight it), Khrushchev at Disneyland.