Cruise companies promote countries & historical sites, but your main experience is ‘The Ship’ itself at sea. So, choose your shore excursions to maximize your travel experience at your most desired site.

A ship’s port arrival & departures are rigidly set, which in turn rigidly constricts the available time for a Shore Excursion's time on-site.  Even large bus tours offer longer & deeper site experiences.

Example: Civitavecchia is the cruise ship port for Rome Shore Excursions. It is 80 km i.e. 2 to 2 1/2 hr round trip of super rushed drives with severely limited time on-sites.

Civitavecchia is 80 km (50 mi) NW of central Rome. Travel time between both, depending on transport mode  (train, bus, Uber, Shuttle) is between  50 min to 1 1/2 hrs depending on traffic.    

SO, if foreign sites & experiences are your TRUE priority, then, you SHOULD consider large bus tours or even better, 'independent self-guided travel.'

Large Bus Touring