We just did a trip to Halong bay, and in one word overrated. The boat was not what we were shown in the pictures, the food was the worst we had in our entire trip. Our guide was incompetent and a scammer. We had the chance to go for a swim when we docked about a 100 metres off Cat Ba Island. Near a floating village. No thank you. We saw where the sewerage from the village went, let alone all the waste from all the neighbouring junks every night. So we asked if we could get off at Cat Ba. We were told "only if you stay at our hotel at $20 each per night" We said that we wanted to stay at the bungalows. He first told us that they were closed down. We replied that another couple stayed there one night before. He then said the weather was no good. Finally he came back and said he could organise it at $45 US each. No way. He then told us we couldn't get off the boat because we didn't agree. Anyway to cut a long story short we got off the boat when it docked and stayed in the bungalow for $15 (for both). Unfourtantley didn't get his name but he had a big mole on the tip of his nose and was as shifty as the day is long.
However our trip overall was fantastic, the people as beautiful as the country. (Found it more friendly down south) But from our point of view, skip the north and you wont miss anything.
We were warned and still got scammed every time we tried anything. It wasn't the price. I knew that the minimum wage in Vietnam is to be $38 a month but it's the principle. Go to Hue and then head back down.