Ranks with the great theaters of the world, like Paris and Buenos Aires. But just try and get a tour reservation! There's a method to reserving, but there's a madness to the method.
There are no online reservations, and no one seems to know how it's done. My favela guide finally said you have to go in the morning in person. I did that, and it was closed. Apparently the magic hour is 10:00, preferably on a day they have tours. Not 9:00. They will be closed and the gates will be locked. Not anytime after 10:00; they will sell out very quickly.
So at 9:50, I got there and joined the queue forming in front of the locked gates, my only hint that I came at the right time. As we waited, we were at least treated to some sidewalk entertainment of a local getting into a fistfight with one of the local homeless guys, with a policeman working to diffuse the situation.
Oh and btw, some days they have tours once a day, and some days thrice. Thursday worked the best when I was there, but that could change on a dime. But whenever you go, know your Portuguese, because there is no English tour. ...except once on Saturday.