It is disappointing when Carnival makes an error like this. The Holiday and the Sensation were obviously put back into service to quickly.
A possible explanation is that this was a first time experiment with the ships being "docked" for 6 months. If you take a complicated huge piece of equipment that already has some 20 years of service under its belt and change its routine for 6 months, things that normally do not break ...will!
Clearly Carnival should have extended the dry dock time by at least two weeks, since it was dealing with an unknown element with this dry dock.
All that being said, there are things that cruisers have a right to expect to be in good working order. The toilet and showers, hot water, and the amenities that were advertised (hot tubs, ping pong etc.)
IMHO, Carnival should be issuing 50% refunds to anyone who had a toilet and shower not fully functional. (not on future cruises, but 50% refund of actual money). With the amenities issues not being up and running, then future discounts of up to 50% (depending on the amount of services the folks were deprived of) should be issued.
To those currently booked, these are my words of wisdom....
hopefully all will be fixed ASAP, however if you encounter difficulties..
For major valid complaints like toilets, showers or lack of water - document it. Then nicely (let me restate that...nicely) go to the Purser's desk and ask for on board credit. Have reasonable expectations for the
amount of credit. If that request is denied, then keep your documentation to write a letter when you get home. Again, don't threaten anyone, if the Purser's desk doesn't sufficiently attend to your request. They all wear name badges, simply note their name so that in your letter you can state that you tried to get settle this on the ship and was unable to do so.
For other amenities (kiddie pool closed, Camp Carnival not up to par, no ping pong tables etc) again document those items which you were looking forward to and that Carnival did not deliver on to list in your letter to corporate when you get home.
If it is necessary to write a letter when you get home, keep it short and to the point. Start off with the good things (and I promise there will be some - even among the worst of cruises unless you are packing a starfish)
then write - "however, the reason for my letter is..."
Keep the complaints to the point. Don't exaggerate or generalize (like all the food was aweful).
I can assure that a reasonable letter will receive a reasonable response.
Don't have unrealistic expectations. They are not going to give you a free cruise, short of the ship sinking.
In all the years of cruising, I am only "type" from personal experience. No cruise has been perfect, but Carnival has always been fair with us whenever we had an issue.
Throwing a childish fit may make you temporarily feel better, but it will not achieve any of the results you really want. (just watch any episode of "Airlines".)
Go and have a good time. And deal with any issues, if and when they happen. And come back and let us know how it went.