Hearts and Minds (new from Worthington Games) might just be the holy grail strategic Viet Nam game I've always wanted. Because it's card-based, there's loads of chrome and history throughout... but because it's done on such a large scale, the entirety of the conflict can be played out in one (long) session.
It handles the two levels of the war very well, with the Viet Cong and political control war being waged side by side with the pure military operations. Victory is generally determined through the accumulation of American Hawk or Dove points, which slide a strategic will marker up and down a track (the US/Allied player wants to keep things Hawkish, and the Communists want the Yanks overwhelmed with Doves). US military losses increase Dove points, for example, while ARVN losses do not.