I have spoken and corresponded with MANY people who have taken one cruise and did not like it and haven't cruised since. The vast majority (I would guess over 80%) booked the "From $599 including air special" from an agent. This means they were in an inside cabin on an older ship and flew down on a charter airline.
These things can be fine but most of the time they are a prescription for a less than enjoyable cruise experience. The cabins are small, the ships are the last to sell out and charter flights can be iffy. (Note: Some charters are better than major airlines)
Also: Many of these are done by bulk agencies that do not offer great, personalized, customer service.
These people had no idea what to expect or any idea what to do once they were on board. They were angry because the cabin was so small, they had to pay for their drinks, shore excursions and were somewhat freaked out about the tips. The documentation helped but it didn't really prepare them.
It really does help to get a personalized agent or be able to do some research and find a cruise that's fits you. Especially if it's your first cruise.