We read all the reviews of Carnival and still decided to sail on the Liberty because it was the only affordable option for the dates we wanted to sail (April 23 - 30, 2011). We had 6 people (2 cabins) and were determined to have a great time.
Overall, we succeeded in our endeavor; however, there were factors that tried to spoil the fun. The biggest issue with the Carnival Liberty was the lack of accountability and willingness to help once mistakes had been made. It was obvious that the culture was to avoid blame and pass the buck whenever possible. An example of this was when our custom ordered dinner didn't get prepared and both the dining room and guest services simply kept pointing fingers at each other. We are vegetarians and the food selection was dismal until we found out we could custom order dinners. This made us happy until we ordered and it didn't happen. Instead of just apologizing and offering solutions, the staff began the blame game. One person even tried to blame us saying we didn't talk to the right person!
Another example of poor service was the lack of service if you weren't swiping your Sail and Sign card. The staff to passenger ratios are already low on the ship, and instead of having all staff focused on the customer experience, they are only focused on their function. This was vastly different from our previous cruises on Norwegian where everyone bent over backwards to serve.
Despite our limited service, we managed to have fun. The kids enjoyed Camp Carnival (day care) and we enjoyed the comedians. The first few nights, the Mambo Kings performed in an open space and we loved to dance; however, they were moved to a lounge where it was just to smokey to go see them.
I would recommend Carnival only to the right crowd - carefree party people who don't care about service as long as the alcohol is flowing. If you expect anything else for the money you pay (service, activities, positive attitudes, etc), Carnival is not the cruiseline for you.