The Deer Hunter - This is this
Character development is not crucial to every film. I'd go as far as to say that, in some films, it's downright unnecessary. But, when a film is lacking in it, it's the first 'flaw' people are able to extract in their adorable analyses. (Horror movies are the biggest scapegoat in this misconception). That aside, it's obviously the focal point & anchor of many films - sometimes successful, sometimes merely adequate, & sometimes missing the mark completely & landing somewhere in vague blandness or, conversely, broad stereotype.
Generally, in the 'character study' sub genre, it takes the span of the entire film to adequately ground its purpose & create a full character arch. The reason it takes this long is because, if it were established too quickly, it'd result in that aforementioned 'caricature crisis.' So, the reason The Deer Hunter is such an amazing achievement is that, in its 3 hr. running time, it establishes its characters thoroughly & eloquently in one 7 minute scene.
Deer Hunter is so rigidly secure in a traditional structure that it's nearly untraditional; there are three acts & each act is stringently divided into their own respective hour. & so not coincidentally, the first act culminates with a scene of (most of) the principal characters preparing to go deer hunting. This 'preparation' acts as a flawless showcase of character development; each man getting their own moment through interaction with the other(s). It's expertly placed within the framework of the film - acting as one final push to create empathy (& sympathy) for where we're going next. But much more so is the achievement in the writing & the performances themselves. It's not at all uncommon to have this kinda scene in a movie -- but to have one this crisp & candid is unrivaled.