They rotate shows around so not all ships are doing the same ones at the same time. A 7-night cruise will have two production shows, two or three headliner shows with a singer, a comedian, and maybe a dance act. On the Rhapsody last month the production shows were "Piano Man" and "Country Time". Kenny James did a singing show, Las Pampas Gauchos did a show, and there was a dance/acrobatic couple.
Cruise ship shows are never over 60 minutes long and the production shows are generally revues, such as with the two we had. Piano Man for example was split into segments with numbers from Billy Joel, Elton John, Ray Charles, Jerry Lee Lewis, and Barry Manilow. The country show was along the same lines but with Dolly Parton songs, etc.