We visited this restaurant pretty much once a day as it was terribly rainy when we visited Hanoi, and it was a few businesses down from our hotel (Tu Linh Palace 2 - which was also excellent). The place is always busy, but even when we went at the peak time and had to head to their third floor dining room, we were served quite quickly.
The best items we had were: the fried soft shell crab with onion and pepper (at 110 000 dong you get two and this is a steal in Vietnam), the grilled eggplant (not the claypot one which we felt was a little on the salty side), the pork ribs (one of the specials of the day), the mixed mushrooms, and the hot and sour seafood soup. If you're there at lunchtime, ask to go to the kitchen to pick out a little bit of everything and you'll have a great variety of food for a reasonable price. The cheapest option would be to get a fried noodle or rice (both are huge portions), but we like variety, so often ordered off the menu and were not disappointed.
It is not high end, you will not have white tablecloths, but you will get a taste of the way locals eat and some really fantastic service.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.