Like Yosemite, the scenery is stunning, but the pictures come out nicer than being there in person. Let me explain. Many have probably seen the bay from pictures and movies (check out episode 4 of Amazing Race sponsored by Travelocity.)
Also like Yosemite, tourist come from all over the world to visit -- Ha Long has already seen over 3M visitors this year and November starts the high season again. That means a lot of tour buses, day trip boats (almost 400), and 70 overnight boats all going to largely the same fishing villages, oyster farms, and cave formations.
I envisioned the overnight trip by kayak and junk would allow us to get away -- think backpacking in the high Sierras versus car camping in Yosemite Valley during high season. However, there's no getting away from the 25 other overnight boats though since we all anchor in the same area -- for protection and regulation. The pictures come out nice enough since you can frame your photos to avoid the masses.
Still it is beautiful, but to appreciate the breathtaking natural beauty you have to come with expectations in order... just like Yosemite valley in Summer with hordes of tourists.