Important: If you want to tour the actual USS Arizona Memorial on the water, you must have a reservation if you do not want to wait in the standby line!! The only place to get those reservations is off of the National Parks website/Recreation.gov. The reason I am adding this is because my friend was ensured he had the right tickets, but it was only for entrance into the main museum area. Therefore, we had to wait in the standby line.
Sometimes, the reservations are hard to get because the site is overloaded (I've heard this from several people), so keep trying. If you do just show up without reservation tickets, the standby line is where you can wait in order to be placed in the boat after those who have reservations have been boarded. Granted, although the boat out to the memorial is a large boat, you can wait quite a while. We ended up waiting three hours, but it was well worth it.
The earlier you get out to the memorial (without having reservation tickets) the better, because you never know how long the line is going to be. This portion of the tour is managed by park rangers and they do an excellent job of keeping everyone sorted and moving through the lines. Please be respectful to them as they're only doing their jobs.
I recommend that if you're not entirely familiar with the history of Pearl Harbor and it's role in the United States' entry into WWII, you go through the museum portion of the memorial before actually going out to visit the memorial itself. There are several films that can be watched along with other exhibits which tell the story about that tragic day. I am a historian and have studied WWII, but I still found this part of the tour helpful as it was a refresher as to what happened that day and sets the stage for stepping onto the actual memorial from the water.
I have no words for the actual memorial itself. To be standing on the place where so many men were entombed was very moving. On the tour I went with, you could almost hear a pin drop until the park ranger began speaking, such a significant gesture of honor and respect for those who perished there. Also, plan to visit the gift shop. There are a lot of neat items in there that you'll want to take home with you. Overall, an excellent, yet hallowing experience.