Been here quite a few times over the last few years. All i can say really is - get into it.
I generally meet up with friends who work just across the way in an office.
My top tip for in the week is if you want to get in for lunch - get there early - you generally need to be in and sat down by 12 midday.
That said once you are in, feast your eyes on the menu. Its extensive to say the least.
Another good idea if you know nothing of Vietnamese food would be to have a look at the menu online first to get an idea of what the dishes comprise of.
I usually have a BunChaGio - basically a noodle base topped with salad and spring rolls. Its so refreshing i just cant stop eating it.
Food is ordered at a glass front counter with dishes on display. They give you a wireless pager which lights up once your food is ready. Its generally very fast - as soon as you help yourself to a cup of tea and select a seat the buzzer lights up and you can get your food.