Magnolia to Boogie Nights to Nashville. The films whose dramatic substance is the interplay across a large set of characters rather than a single protagonist arc.
The ensemble film is structurally distinct from the single-protagonist film. The dramatic substance comes from the interplay across multiple characters rather than from one protagonist's arc. The form is harder than it looks — directors must give each major character enough screen time and dramatic substance that the audience can track them, while keeping the cumulative narrative coherent.
Our picks across the form.
Successful ensemble films require unusual screenwriting and editing discipline. Each major character must have enough screen time and dramatic substance that the audience can track them and care about their arc. The cumulative narrative must be coherent — the audience must understand how the separate storylines connect to each other thematically even when they do not connect literally. The runtime is typically longer (Magnolia is three hours, Nashville is two hours forty minutes); the form does not, in general, fit conventional 90-minute runtime.
The directors who have succeeded at the ensemble form are typically those with strong individual relationships with multiple working actors. Robert Altman could call on a stable of regular collaborators across decades. Paul Thomas Anderson developed his ensemble through the back-to-back productions of Hard Eight, Boogie Nights, and Magnolia. The casting precision is, in some sense, the foundation of the dramatic precision.