I stayed at the Marriott – North Bethesda for four nights in early May, where I chaperoned four high school students at the National Junior Science and Humanities Symposium. The hotel and the attached convention center are modern and attractive. This is a great place to come if you have business at the National Institutes of Health, which is just a few miles down the road, or if you are attending a convention (as I was) or attending a Bat Mitzvah (as was also in evidence that weekend). It is not a place to go for a vacation. Even though a subway stop is in very easy walking distance, I think one could find a more interesting place to stay for less money if you wanted easy access to the Washington subway system.
The food at the convention center was excellent, and all four of my students agreed that the food was very good. The rooms were perfectly adequate, although you will not find a safe in your room (at least there was none in mine).
The area surrounding the hotel is not particularly attractive, but it is not urban blight either. It is a safe area, and I had no reservations in allowing my student delegation to walk to the nearby strip mall, or to the subway stop to go to the Washington Zoo and the National Mall.