Ratings are generally compiled by professional cruise critics or by tourists who have completed their trip and want to share their experiences. While anyone can have a bad experience for reasons that are out of the control of the cruise line, compiling a large number of ratings can give potential travelers a good idea of the average enjoyment level that other people have had. It helps them anticipate the kind of experience that they will have on board the ship.
Many websites and guidebooks that offer ratings also include in-depth reports so that readers can get an idea of why the cruise received the score that it did. This also helps to determine whether a negative experience was a one-time event (for example, if stormy weather caused a vacationer to have a bad time on their trip) or more endemic of that particular cruise line.