Congratulations on booking your first cruise! It is truly a very exciting time and you will likely have the time of your life.
Don't listen to any naysayers...especially those who have never even sailed Carnival. My first four cruises were all on Royal Caribbean and I thought I would never sail another line, but out of convenience, I took my family on a back-to-back cruise on the Carnival Elation out of Mobile, and we absolutely loved it and had the best cruise ever. Since then we have sailed multiple cruises on both Carnival and Royal Caribbean, and I must admit that it seems like my family prefers Carnival. To us, it just seems that the cruise director staff draws us in to the activities better...we can't really put our fingers on it, but we all noticed it.
Anyway, have a great time!!!