Busara's in Tysons and Reston
Tysons one is pretty bad :-(. I've not been to the Reston one.
I've been to the Tyson's one several times lately, and have been consistently disappointed. Environment & service are fine -- the food just isn't great.
And there are plenty of other better Thai options in the area -- Neisha Thai, Thai Pilin, even Natta Thai if you are willing to go an extra couple miles into Vienna.
Another good "similar" option in Tysons would be Taste of Saigon.