My in laws did one and it was terrible. It was a Carnival cruise on an older ship (MIL referred to it as a barge). The plumbing in their room broke on the first night and they waded through three inches of water for the rest of the cruise. The ship was full so they couldn't change cabins. The water was really rough, and the ship being older didn't have the modern stabilizers taht they build in now, and MIL was ill the entire time. The food, though plentiful, was terrible, and some pax came down with food poisoning.
The experience was SO bad, they'll never cruise again.
Anne