Okinawa-hontō is the largest island in the Southwest Islands, and the historical seat of power of the Ryūkyū dynasty. Although its cultural differences with mainland Japan were once evident in its architecture, almost all traces were completely obliterated in WWII. Fortunately, Allied bombing wasn't powerful enough to completely stamp out other remnants of Okinawan culture, and today the island is home to a unique culinary, artistic and musical tradition.
The island is also home to some excellent beaches, delicious food and friendly people, many of whom speak a little more English than their mainland counterparts. Of course, with US Air Force jets flying overhead from time to time, it's hard to forget the reality of the continuing American military presence on the island and the history behind that presence.
Prefectural capital Naha is a transportation hub for the other islands. War memorials are clustered in the south of the island, while there are some good beaches and other attractions on the Motobu peninsula. The north is relatively undeveloped.
It's worth noting that Okinawa-hontō has been somewhat overdeveloped for domestic tourism. If you seek Southeast Asian–style beaches and fewer big resorts, the majority of your time is best spent on Okinawa Prefecture's smaller islands.