I visited Ha Long Bay as a side trip to a bicycle tour of Vietnam. We stayed overnight on the bay and took a kayak tour the next morning. The boat itself was first class and the service and meals on the boat were excellent.
Unfortunately, it's my opinion that this should be taken off of the list of World Heritage sites. Why in one word: POLLUTION. Not only is the air so thick with pollution that it's difficult to see the beautiful limestone outcrops jetting out of the bay, the water stinks to the point where I was concerned about it splashing on me when we kayaked. It seems to me that the 100's of boats in the bay may be dumping raw sewage into it. What a terrible shame and truly an environmental disaster. The Vietnamese government is spending a bundle of money widening the roads and building a new port area so people will visit. Unless they also turn their efforts into cleaning the area up, they might as well leave the roads alone. Furthermore, from what I could see, it will take 15-20 years to clean this site up. Too bad-- the decimation of this site is impossible for me to understand.