My wife and I always do the Hop On/Hop Off bus tour whenever we get to a new city. It's a great way to get oriented and find out where some of the major attractions are so that we can go back to them later. We were somewhat disappointed in the Madrid version of Hop On/Hop Off in that the commentary never seemed to be in sync with what we were passing at the time. Also, the busses did not come close to staying on schedule and in one instance, we waited for almost 45 minutes for a bus to come pick us up.
Having said that, the bus does 2 different loops through Madrid and it will take you about 1 1/2 hours to do them both, non-stop and it is a good way to get oriented to the city.More