We stayed three days on Oahu, with our main destination being Pearl Harbor. Pearl Harbor is a museum, a memorial, and an experience.
When you arrive and find a place to park, don't pack up your camera bag and purse. All bags must be left in the car or at your hotel. You may bring your camera in, though. There is an audio tour for the museum for a nominal fee. The audio tour helps to bring the museum to life and is the only fee you will need to pay, as the rest of your visit is free.
As you enter the museum, you will receive a ticket for the boat ride into the harbor to see the Arizona. When it is time for your group to go, you will be directed into a theater to watch a short movie about the attack on Pearl Harbor, then out a side door to the boat that will take you across the harbor. It is a striking image to see the stark white Arizona Memorial with the bright red, white, and blue flag whipping in the wind above it. The Arizona is just below the water, and the rusty red bulk is like a shadow in the dark water. There is a marble wall inside with the names of all those who were lost carved into it. You get about 10 minutes at the memorial, it is a quiet time of reverence. There you will find everything from detailed information about the attack to personal belongings and letters of a soldier who died that day. You can take as much time as you want in the museum, and next to it is a gift store with some good books and other neat items.
It is a powerful thing to see, and I wouldn't have missed it. I thought it would be a lot more emotional, but maybe my expectations were too high. I recommend that you take two or three hours to see this piece of American history.