As for Waikiki, its grossly overrated... Get out of there and enjoy the more remote parts of the island.
I agree with this. Waikiki is tourist-central. There are *so* many places that are prettier and more like "real Hawai'i".
If a person is going to Oahu, I generally recommend a couple of things.
-- a "tourist day". Walk along Waikiki beach, enjoy the sights. Maybe take a surfing class down by the Outrigger. etc. Hike to the top of Diamond Head if you feel like it - go very early in the day, if you do, it gets hot, but the view is awesome. Bring water. I used to suggest spending time wandering through the International Marketplace; sad that it's gone now.
-- a "history" day. Pearl Harbor, Arizona Memorial, tour of the Missouri, etc. The Bowfin is cool, too. Then head to Iolani Palace, the Mission House museum or the Hawaii Maritime Center. If you want to make a day of it, head to the Bishop museum. Be sure to spend lots of time outside, though, no point in being in Hawaii if you're going to stay indoors all day.
-- a "scenery" day - drive over the mountains on the Pali Highway toward Kaneohe. At the coast, turn right to go to Blowhole, Koko Head, Hanauma Bay... or left to go up the coast toward the Polynesian Cultural Center (which is *very* touristy, but still sorta interesting). Fortify yourselves on the way with a stop at Cinnamon's restaurant/bakery in Kailua
-- and, a "relax" day - drive up through the pineapple fields, stop at the Dole center on the way, then follow Kamehaha Highway to Haleiwa. Have a plate lunch, be sure to get a shave ice at Matsumotos, then meander up the north shore enjoying the laid-back feel (and, this time of year, maybe even some big-wave surfers to watch). Find a beach that appeals to you and chill for a while. Then cruise up to Waimea Falls park, and maybe a nice sunset dinner at the Turtle Bay resort...
MANY other things to do. And lots of things worth re-doing. But... at least that'll give you a range of stuff and give you a sense of what the island has to offer.
Oh, and if you like seafood? Definitely get out of Waikiki. The restaurants (especially along the beach) are both touristy and expensive. The hole-in-the wall places (shrimp trucks, small poke shops, sushi, etc) will "break your mouth" ;-)
