(Please note, I am not a native english speaker. My first language is french, so some of the words or expressions used might be odd!)
I've never considered doing a cruise in my life. To me, walking in Paris, London or New-York, discovering those cities, would always be preferable to being stuck with other tourists on a boat, visiting for an hour or so a small city, all bunched up together.
That view changed drastically in 2006, when I did my first cruise, with my wife, on the Celebrity Millennium. Despite having access to a cruise boat all summer, we feared back then that we might be sea sick, and decided to take a cabin on the low level of the ship, in the middle. That way, we would feel the waves a little less. That trip on the Millennium, in the eastern caribbean was simply amazing. And we never once got sea sick.