My girlfriend and I stayed here on the second night of our 3 day/2 night Halong Bay boat tour. I don't know the price for a night here because it was included in the tour price, so keep that in mind if you plan to give my below review any merit.
Anyway, with that caveat, the hotel was great. And it is a big "sterile" hotel, so don't stay here if that is not your thing. The room was spacious, clean, and had a nice balcony overlooking Cat Ba bay. The bed was comfortable, the sheets were clean, and the flat-screen TV had a few English-language channels to watch as you drift off to sleep. Both the front desk and other staff were also friendly. The in-hotel restaurant was OK (again, however, we did not pay because it was included in the tour price), but I suspect you could round up tastier seafood down the street.
Cat Ba town itself is more or less a one street town, but its ocean front street is nice to stroll down. There is not much "nightlife" to speak of if you are looking to go out, particularly at the Hung Long Bar connected to the hotel (I was the only one there when I stopped to have a beer). If you do spend a night in Cat Ba town, the best thing to do is go walk up the hill behind the hotel and hit up the nearby local beach. It is only a five minute walk.
All in all, I really liked the Hung Long Hotel. Particularly because it was included in the price of our Halong Bay boat tour.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.