Which Carnival ships were you on for the first two cruises?
For what it is worth, if timeliness and personalized service are as important to you as you say (and I agree with you), then there are certainly plenty of other cruise lines to try.
Carnival has it own special charm with super friendly waiters who sing, dance, do tricks, etc. But Carnival in general has more passengers per crewmember than other cruise lines (known and crew/passenger ratio).
I am sorry you had a bad cruise, but it just happens sometimes. The one thing I usually recommend is that if someone is unhappy during the cruise make a change in tables/waiters before the end of the cruise, because once the cruise is over there is nothing one can do to salvage it.