I'm quite convinced that the location of the hotel is the primary determining factor for the category. I've stayed in some pretty mediocre looking rooms in pretty ordinary looking hotels ranked as category 5 and up. Those hotels were in prime destination cities. I've stayed in delightful rooms in marvelous hotels ranked as low as category 3. These were in less popular locations. It looks like if it's in the right location, it's a minimum of category 5.