Just got back from Halong Bay and we booked overnight stay on the Paradise Explorer. Good 4 star experience and we had the all inclusive package for food and drink.
It took us about 2.5hrs from Hanoi and it was a very pleasant drive. Halong Bay is very clean and the water is beautiful. It was cloudy and a bit chilly so we didn’t get into the water.
They took us to a cave which was extremely packed with tourist so we decided to skip the tour and just people watched. Another tour was a pearl farm which we decided to stay onboard.
In the evening, the boat comes back towards the harbor and anchors in the middle of sea. You sleep on the boat which has very comfortable rooms and bathrooms and in the morning, the boat heads back in. They have some excursions in the morning but due to the weather, everyone chose to stay on board.
Food was really tasty and drinks were good. I would recommend an overnight stay but 2/3 days is really pushing it.