If there was one piece of London I feel like I could have skipped, this it it. Everyone says you have to go see the Changing or you're missing out, but I disagree.
The main problem with the Changing of the Guard is the crowd. There is simply no way to properly view the ceremony unless you arrive an hour or more early. And since it takes place at 11:30am, you are spending some of the most valuable parts of your day just waiting.
The ceremony itself is quite impressive. There is music and a flurry of organized movement. I was impressed with the ceremony itself, even if I was only wondering how they keep cool in their uniforms. If you've got other places to be in London, though, skip the Changing of the Guard.