The play is not nearly as socially relevant as 40(!) years ago, meaning it can now not be much more than a good show. But it is a very good show.
The Shakespeare references are enjoyable, although the plot is not always too obvious.
And in the end, a voice over announcing president Bush's (nice Hair reference in itself) decision to send another 20.000 souls to Iraq makes for a reasonable attempt to draw a parallel between the '60s and '70s public dissent against the Vietnam war and the current dissent against the war in Iraq.
Wikipedia has an interesting article with background info on the original play.