Straight from the website:
In March 30, 1902, a story in the New York Herald described Whitehall, the Palm Beach home of Henry Flagler as, "More wonderful than any palace in Europe, grander and more magnificent than any other private dwelling in the world..."Flagler built the 75-room, 100,000-square-foot Gilded Age mansion, Whitehall, as a wedding present for his wife, Mary Lily Kenan Flagler. The couple used the home as a winter retreat from 1902 until Flagler's death in 1913, establishing the Palm Beach season for the wealthy of the Gilded Age.
Henry Flagler, founder of Standard Oil, is a huge figure here in Palm Beach County. From Wikipedia:
He was also a key figure in the development of the Atlantic coast of Florida and founder of what became the Florida East Coast Railway. He is known as the father of Miami, Florida, and founded the city of Palm Beach.
I do think the Flagler Museum is worth a trip, although typically I'm not into museums or history. It was most certainly opulent! The word that came to mind when I walked up to the impressive building was "GRAND."
Instead of writing a lot about it, I just recommend that you go yourself, even paying the full admission price. I do think it's a good idea to take a tour, and take your time there, instead of rushing through it in 45 minutes like I did (a challenging thing to do with the large crowds-- but I managed!).