There's not a product in the world that can present specifically what it delivers in a 15 or 30 second advertisment.
They are advertising a "brand". What expectations you establish for yourself based on their advertising is really quite individual.
However, if someone has an experience that is an obvious flaw, and generally unsatisfactory, I see no problem with them "griping" about it.
I think you'll notice the majority of the "gripes" about cruises are about people's fellow passengers, more so than failures of the cruise lines.