Terrific! For the cost it was very good. We did rent iPad devices in the Duomo which we suggest for viewing the Duomo itself, the Crypt and Museum and Bapistry. As this was not really a tour we just received discount tickets.
It was not a busy day at the Duomo of Siena on the day of my visit, so there was no line to skip. This is probably because I went at the beginning of the holiday season in Italy. I would still recommend people to purchase the Skip-the-line Entry Ticket just to be sure, especially if you plan to visit Europe from mid June to late September.