Great race through D.C. It is a very pretty course through the city. You will spend some time running on the expressway and that wasn't my favorite. Not too difficult as far as hills.
This is a BIG race (over 30,000) so be prepared for congestion. The race itself was fine but getting to and from the race was very tough. The metro was extremely crowded and you had to walk a long way.

Other than that - fun race! I'd do it again.