Liberty was our 39th cruise in last 10 years, 4th with Carnival, and 2nd out of 6 for 2010. We are a retired mid-50's couple who lives in Florida and loves to cruise.
Ship is more tastefully decorated than many of the Carnival ships. Food was very good in dining room for dinner, buffet was average, except for the Mongolian Grille which was excellent. We experienced the usual Carnival Eggs Benedict problem with the yolks being over cooked for breakfast in the dining room. My approach was to ask for soft centers and just keep sending it back until they got it right.
Our main concern with Carnival is entertainment. Liberty was above average for Carnival for the singers and dancers, but still a step below what we experience on the large RCCL ships, NCL Jewel class ships, and Celebrity Solstice class ships. Carnival has chosen to have only 1 male and 1 female singer and dancers that are not above average. The shows are the same shows with little change over time. Carnival's production shows lack the acrobatics and featured acts we find with the other cruise lines. Pool bands generally consist of 2 people and a bunch of electronics, somehow this falls short of being a band that generally has 4-6 members.
If you just want to get away, have good food, are not overly concerned about entertainment quality, and want travel a little less expensively Carnival is a great choice. However, if entertainment is very important to your cruising experience we would have to recommend the other cruise lines mentioned above.