I LOVED Olbia. It was my favorite place! We took the tour to Madellana and thought it was beautiful. I really enjoyed lounging on the beach with my family instead of going to see ruins of some sort.
The biggest recommendation that I have is to make SURE you get there a couple of days early. I can't count the number of people whose luggage was lost and NEVER got it the entire cruise! Make sure you swap clothes between bags so at least if one bag shows up, you have a few days of clothes instead of NONE.
I did not have any problems with the tours, I enjoyed them all. I agree that there was not much time to shop, but I really didn't go there to shop so I was not disappointed. I felt like we would get back at a reasonable hour in time to relax before the late seating and have a swim. My son enjoyed the camp so much we could never get him out of it!
My biggest disappointment was Pisa. Skip it and stay in Florence longer!