I'm currently in Rome and today we did the Vatican Museums guided tour in Spanish. The whole place was packed, but that's probably because many of us went to the museums straight from the general audience with the Pope, which is always on Wednesday mornings.

The guide was an Italian woman on her 50s who spoke fantastic Spanish and took us through most of the museum landmarks in 2 hours. She made some silly mistakes (e.g. when explaining "The School of Athens", she said "Socrates, about whom we know so little because he didn't like writing..." – Madame and I stared at each other for a few seconds and cross-checked whether we had heard the same), but overall I think taking the guide was worth it. Not only did we avoid the queues as we had already booked online, but also the Vatican Museums are huge and quite unfriendly when compared to the Louvre, the Pergamon in Berlin and the British Museum, so it was better to have someone taking us across the place. After the tour we did stay for a few more hours to see all the other parts that interested us but weren't covered by the guide.

Re the Sistine Chapel, I agree with Perche – they tell you it is a place of worship but it has the spiritual contents of a crowded train station.