They all pretty much offer the same. Theater, bars, casino, pool, buffets, restaurants etc... The differences is in the sizes, layouts and decor and that's really what makes it exiting to cruise the different ships. Carnivals ships are grouped into different classes where the ships in each class has almost the same size and layout, but different decor.
There is a great description of all Carnivals classes and ships on Wikipedia here
So if you want to experience the difference in the ships then you'll make sure to cruise on another class on your next cruise.
My cruises:Carnival Fantasy 9/7/06 Nassau/Half Moon Cay, Cabin V26, 4 nights Carnival Inspiration 3/17/07 Grand Cayman/Calica, Cabin R132, 5 nights Sovereign of The Seas 12/21/07 Nassau/Cococay, Cabin 8568, 3 nights Carnival Glory 6/14/08 Cozumel/Belize/Roatan/Freeport, Cabin 6481, 7 nights Carnival Liberty 5/30/09 Ocho Rios/Grand Cayman/Roatan, Cabin 8229, 7 nights Monarch of The Seas 09/21/09 Nassau/Cococay, Cabin 5529, 4 nights Majesty of The Seas 06/14/10 Key West/Nassau/Cococay, Cabin 9506, 4 nights Carnival Legend 10/03/10 Grand Cayman/Cozumel/Roatan/Belize, Cabin 5181, 7 nights Freedom of the Seas 11/28/10 Labadee, Haiti, Cabin 9489, 4 nights Carnival Freedom 08/26/2011 Colon/Cozumel/Limon, Cabin 8425, 8 nights Carnival Sensation 01/15/12 Freeport, Nassau, Cabin E37, 4 nights Carnival Imagination 02/13/12 Key West, Cozumel Cabin V32, 4 nights Carnival Sensation 09/09/12 Freeport, Nassau, Cabin U18, 4 nights Caribbean Princess 02/09/13 Princess Cay, Curacoa, Aruba, Cabin C623, 7 nights
Yes, although most of the activities are the same, shows, pool area, etc... may be more elaborate on the larger ships. Even the passengers may differ from one ship to another - longer cruises vs. shorter cruises. Even when you travel makes a difference. Around shool holidays you will have many more kids and families onboard. The bigger ships are newer with newer technology. Find a ship class that you like - not what someone like me likes. I perfer to look at the itinerary and cost when deciding. But, then again, I booked the Breeze Transatlantic just to experience the new ship. This time that was all that influenced me.
Some Carnival ships have features others don't. For example, none of the Fantasy Class ships(Carnival Fantasy, Imagination, etc) and the Spirit Class ships(Carnival Spirit, Pride, Legend, Miracle) have the Carnival Seaside Theater which is the large outdoor movie screen over the midship pool. The Fantasy Class ships, Destiny Class, and Triumph Class ships(Carnival Triumph & Victory) do not have Steakhouses(Specialty Dining).
2004:Carnival Destiny, 2005:Carnival Valor, 2006:Crown Princess, 2007:Costa Magica, 2007:Azamara Journey, 2008:Celebrity Century, 2008:Norwegian Sun, 2008:Carnival Splendor, 2009:Navigator of the Seas, 2009:Carnival Imagination, 2009: Ruby Princess, 2010: MSC Poesia, 2010: Norwegian Pearl, 2010: Carnival Imagination, 2011: Norwegian Sky, 2011: Holland America Line Eurodam, 2012: Carnival Miracle, 2012: Celebrity Millennium, 2012: Carnival Breeze