I was going through a list of Oscar winners and was surprised to see that this film beat Butch Cassidy and the Sundance Kid for best picture in 1969. After actually seeing it, however, I'm not surprised anymore. It was way ahead of its time in regards to its style, cinematography, and use of flashback to help develop Joe Buck's character.
The most amazing thing to me is the depth of Joe Buck's character in such a short movie. I think Voight captured the naivete and the viciousness-when-provoked. The two scenes that really caught me were after he gets the blowjob in the theater and when the older man solicits him. I think when he looks in the mirror he's trying to see if it's really him that has done- or is about to do- something terrible.
I think it was a brilliant decision by Hoffman to take this role. Otherwise he may have been typecast after the Graduate. Anyway, this considered an all-time great for a reason.