Oahu has plenty of highlights to keep you amused.   If it's winter then a visit to the North Shore is a must, to see the surfers doing their thing on the enormous waves.   You'll see why this is the world mecca for surfing.   Unfortunately I wasn't there for the really big waves, but the surfing's still pretty good compared to most places around the world.
    There are plenty of other interesting things to see, and for many people a visit to Pearl Harbor is a must.   Japan's first strike against the United States during world war two makes this an historical location of world-wide importance.   Most people know of the memorial which commemorates the destruction of the battleship USS Arizona during this attack, but you can also visit another American battleship, the USS Missouri, which symbolizes the end of the world in the Pacific, since it is the place where the Japanese signed the documents of surrender at the end of the war.   You can tour its decks, see the place where the surrender instrument was signed, and even see where a kamikaze pilot died in a fruitless attempt to sink the ship.   Still on a military theme, not too many people know of the USS Bowfin submarine museum which is also at Pearl Harbor, right next door to the USS Arizona visitor center.   You can tour through the Bowfin, a submarine which entered service a year to the day after the Pearl Harbor attack and became known as the "Pearl Harbor Avenger" by sinking 44 Japanese ships.   You can also see a Japanese "kaiten" kamikaze submarine, as well as American post-war technology including missiles and torpedoes like the Mark 45, which carried a nuclear warhead.

   The Big Island of Hawaii appealed most as my next destination, mainly because of the active volcano, Kilauea, but also because of the good snorkelling and more minor features like Ka Lea, the Southernmost Point in the USA.   The Big Island also has interesting history, both native Hawaiian and as the place where the famous English explorer Captain Cook was killed.   Captain Cook is strongly associated with New Zealand, he's even on some of the money, so for a New Zealander this event has special interest.