Hai Duong is nothing fancy -- the plain tables and lack of decor speak more of a cafeteria than a sit-down restaurant -- but it's a convenient and tasty option among the wide array of Eden Center food options. The menu is large and has all the standard options you'd expect to find as well as those that don't usually make an appearance in those restaurants aimed exclusively at a Western clientele (think organ meat). But it's easy to look at photos and order by number.
As another reviewer noted, the service is typical for a casual Asian establishment (meaning a local one in Asia, not a restaurant in downtown DC that serves Asian food). When you walk in, someone tells you to choose your own table, and after a few minutes, someone will come by to take your order. After you eat, you leave your table and pay at the register at the front of the restaurant.
Hai Duong seems to get a variety of patrons -- Vietnamese families, groups of young adults, a few couples. It can easily accommodate large groups, and the food comes out quickly. I'd recommend it as a casual place when you're craving some Vietnamese food with friends (not really a date spot).