This http://www.halongplaza.com/home.htm was about as good as it could get in Halong Bay. We stayed there when it was brand new (4-5years ago) with nice beige carpets and full marble bathroom. The room was actually much nicer than that shown on their website, and it exceeded our expectations. I would rate it as 3.5 star (when it was brand new).

There were several new hotels under construction then but I have not heard of any "luxury" option so far apart from the Sheraton which is not due to open until 2010. Maybe be worthwhile looking for a luxury junk instead.