I had an opportunity to go two Mays ago.
I loved it, the history is unbelievable.
Unfortunately very crowed, and there is no way to linger and look at the art, as everyone is sort of rushed along. You can linger a bit in the Chapel, but those guards will get you if you speak above a whisper.
We went to Peter’s Church, just as beautiful and only a handful of people.
If you ever go back I’d recommend the week before Christmas and stay through Midnight Mass.
I had the whole city to myself because pilgrims don’t show up until the 23rd and a lot of Italians are already on holiday.