There are a few notable exceptions to three-act structure.
So-called Art films often experiment with convention in interesting ways to find entirely different methods of telling a story. But usually the only people interested in watching these are film buffs. These aren’t very mainstream, and do not make much money.
Some crime films feature unconventional narratives. In this case, it could be that the realism of the subject matter allows the writers to play around with structure, whereas a story in a more fantastic setting would require a more straightforward plot. Most filmgoers are also familiar with straightforward crime movies, which means that we would understand when a writer departs from the norm, and how the story is unusual. As a result, Quentin Tarantino can use Pulp Fiction to tell three interrelated stories in non-chronological order, and Christopher Nolan can tell Memento backwards, to reflect the main character’s condition (short-term memory loss). Films like Sergio Leone’s Once Upon a Time in America and Fernando Meirelless’s City of God also have a narrative that jumps back and forth through time.
Some other films dealing with gritter contemporary subject matter also play around with chronology, often with seemingly unconnected stories that are all revealed to be intertwined. Guillermo Arriaga did this in two of his films, 21 Grams and Babel. Usually, it’s not until the end of the film that you realize that anything has been told out of order. The unconventional structure serves to hide a twist in the narrative.
Some adventure films feature more than three acts. Usually this would be one in which a hero travels through the world looking for clues to help him on a mission. Examples would be the Indiana Jones films or the Da Vinci Code. In Story, McKee would argue that each new location sets up a new act which ends when the protagonist finds a clue that will send him to the next location and the next act.
These adventure films tend to feature characters who don’t really grow much over the course of a film. Hell, the second Indiana Jones film was set prior to the first, an indication that he hadn’t changed in any significant way during Raiders of the Lost Ark. This type of narrative may also be part of a dying trend.
In Everything Bad is Good For You, Steven Johnson noted the ways in which storytelling in pop culture has gotten more and more complex, comparing the narrative of the Star Wars trilogy to the Lord of the Rings trilogy. Audiences are primed to expect more character arcs, which writers and directors are providing. Compare the earlier James Bond films to the Daniel Craig movies. Hell, Indiana Jones had a major character arc in Kingdom of the Crystal Skull, even if that wasn’t exactly an improvement over the original.