I'm Canadian, so I have never really felt a sense of patriotism or connectedness to American-produced historical war movies or tv shows. I've felt that any that I've ever watched go through a process of trying to justify American involvement, or cast the Americans in a favorable light.
Tour of Duty is special in that you aren't required to have any knowledge of the context surrounding the Vietnam War. Although the show focuses on a platoon of American soldiers and their hardships, it also gives a strong sense of the hardships endured by the other factions involved in the Vietnam War. It gives a true sense of what was felt by all, and really gives a different perspective on the events that transpired.
Tour of Duty doesn't succeed due to the fact that it has incredible acting, impressive special effects, or nudity. That isn't to say that the acting isn't good or the set backgrounds aren't interesting. However, the true strength of Tour of Duty is experienced through it's ability to portray emotion, and induce emotion on the viewer. It's weird, but that simple fact is what makes this show better than anything else I've ever seen on TV.
Although the series only lasts 3 seasons, it is definitely a must-see for anyone who takes TV shows seriously. Some presumed financial difficulties result in the latter half of the third season feeling diluted, but the rest of the series more than compensates, for an overall experience that truly defines it's genre on television.