The LA Times wrote a good article about what it takes to reach a 5 Star rating with Forbes Travel. According to the LA Times:
It may not come as a surprise that California — a sun-splashed magnet for celebrities and big-spending tourists — leads the nation with the number of hotels winning five-star ratings from Forbes Travel Guide. But winning the coveted rating is no easy feat. Only 58 hotels in the U.S. — 12 in California — were awarded the recognition this year, including, for the first time, the Resort at Pelican Hill in Newport Beach.
The Forbes five-star rating is considered more difficult to land than the five-diamond rating from AAA, which awarded its top ranking to 101 hotels in the U.S. this year.
Hotel owners vie for the Forbes distinction because it enables them to charge much higher rates. For example, the four-star Beverly Hilton recently posted average daily rates of $245 to $325, while the five-star rated Beverly Hills Hotel posted rates of $510 to $540.
The main difference between a 4-star hotel and a 5-star hotel is typically guest service and amenities. From the article: