Paul,
We have been on several cruises, Norway, Baltic, Adriatic and Alaska, Transatlantic plus Rhine and Nile river cruises.
Just normal people on board.
You need to choose carefully but it can be a great way to take a holiday. Norway is good because you get to see the Fjords from sea level and don't have to suffer the eyewateringly expensive onshore prices of food and drink. The Baltc was great as how else would you visit so many different countries in such a short space of time, Sweden, Estonia, Russia, Finland, Germany and Denmark. St Petersburg is amazing.
Adriatic: Corfu, Venice, Dubrovnik, Split etc. All great places to visit. Alaska: the inside passage from Vancouver taking in spectacular glaciers which can only be seen from seaward.
Transatlantic: on Cunard's QM2, a real Ocean liner with New York at the other end.
Rhine to Basle, all that history along the banks with calls at Cologne and Strasbourg.
River Nile: simply unforgettable, we have done it twice now.
All wonderful expreriences and worth every penny.
Colin