*shows age* I think it was made in 1978 and was one of the first films about vietnam and certainly one of the earliest "statements" that was sympathetic to the returning vets. Much US public opinion was opposed to the war, Nixon, and the returning soldiers. In fairness to younger posters here who struggle with the slow early pace, it might help that perhaps Cimino had to work to build empathy with his characters, show them as ordinary people, in order for the audience to care for and fear for them when things went pete tong / viet cong later in the film.
Now - there are plenty of vietnam films. And the networks don't like to schedule a three hour movie, certainly not when they want to pad it further with adverts.
These days, a younger film fan would already have seen apocalypse now, born on the 4th of july, full metal jacket, good morning vietnam, vietcong christina barcelona, before seeing the deer hunter...and I think it helps to know the context of deer hunter to give it a chance.
A film should stand alone on its merits without apology or overexplanation- I still think it does. A great film can work decades later, and can also parachute you into the time in which they were made.