Just got back, here's my short review. We did a 7-day cruise on the Carnival Liberty out of Miami and into the Western Caribbean (Cozumel, Belize, Roatan, Grand Cayman).
Food - This was the big thing for me, the food. The Liberty has a Guy Fieri's Burger Joint that operates from 12-6 daily and is free. The burgers are definitely better than fast food and pretty tasty overall. I'd pay fast food prices but not much more. If you order a plain cheeseburger you can add your own toppings at a topping bar and the burger is handed to you almost immediately. If you want them to make it, you could wait up to 5 minutes. The buffet area was mostly filled with black people and the food was depressing. The steak is definitely the "poorer" cuts and you can tell it is almost always the stuff the steakhouse wouldn't use. Speaking of the steakhouse, for $35/pp it wasn't too bad. The steak was good but the food is really high-class and upscale - I didn't understand most of it. If you're into that stuff it's probably great, but for us it was too high class. The formal dining area was pretty decent, but I felt they were trying too hard. Just give me a steak and mashed potatoes and I'm happy. 7/10
Decor - Ship looks really dated on the inside. Lots of neons, lots of older furniture, lots of dingy looking fixtures. The rooms were ok, but the beds smelled funny and were hard as a rock. Everything just seemed like it belonged in the early 90's. 6/10
Shows - Adult comedy was really good. I don't remember the comedians but we had 4 different ones and they were pretty good. Tough to get seating at the club, we had to generally show up around 45 minutes before showtime for any hope of a seat. The other shows were boring. A lot of musicals, a lot of partying on the Lido deck, and that was about it. I found myself reading on a deck chair most nights. I'll give it 8/10 for the comedy and the fact that others seemed to enjoy the shows.
General experience - I had a great time, but it wasn't the ship that attributed to that. Although I enjoyed it, I didn't find the appeal that most people have. The ports and excursions we chose (through Orbitz, not though the cruiseline) were amazing and are unforgettable, the ship however is forgettable. Several things really detracted from our trip: too many kids, too many rude ass people, too many black people that thought they were millionaires and being assholes, and too many college kids. I suppose we should've picked another cruiseline from the reviews, but it still wasn't too bad. 7/10
Most likely won't be cruising Carnival again, if any.