We were on the Med Odyssey last April. You will love it!! Some ports may have changed, as we did not stop in Chiogga. We took mostly included tours, too, but highlights of the optional tours we took are:
Nice, Eze & Monte Carlo excursion was a highlight. Full day and so enjoyable. Definitely one of our favorites. Quite a bit of walking, including steep hills and cobblestones.
Tuscany to Pisa. We did this in place of the included tour to Florence, because we were going on the post-extension in Tuscany which included much better touring of Florence. We enjoyed seeing Pisa and the leaning tower
Sistine Chapel & Vatican City. This was a must-see for me. Was not disappointed
Pompeii: Did this on advice of others. Highly recommend
Evening Gondola Ride: Viking did not handle the logistics of this well. Between issues with docking outside of Venice, bussing/boating us in and being one of the first tours coming out of the pandemic, it was very messy to say the least. However, we did enjoy this very "touristy" excursion and can now say we experienced it.
The biggest surprise of the trip was how beautiful Corfu and the 2 stops in Croatia were. You will love this cruise!!!