I just visited Washington and ate at Corduroy, Mokoto, and Oyamel. I provide more extensive info about them on my website, but let me provide a summary here.
I really enjoyed Corduroy. It is a really comfortable restaurant with excellent, although not superb, food. If you like ordering small portions of multiple courses, this isn't the place for you. There is a first course, a second main one, and dessert if you wish. The servings are rather large. The wine list is terrific.
It was my second time to Mokoto and I had to be talked into going back by my mate, who wanted to give it a second chance. I won't go back. The food is not very good (except the sashimi) and the restaurant is very uncomfortable.
Oyamel has long been a favorite of mine when I just wanted simple, but well-spiced tapas-style Mexican food. I think it serves really excellent dishes and the quality has not diminished despite its increasing popularity.