Mrs. REL and I have done 4 cruises, all with Carnival. Nothing really wrong with them, we enjoyed them at the time. However, having said that, we are probably not going to do another Carnival Cruise again. They were enjoyable when we were younger (still in grad school before kids.) But now that we are both making good money we will probably do RCL or Disney, then check out Princess or Celebrity when we are older and don't need the more "kiddie" activities.
I will say this, if you have a job where, even on vacation, people tend to like to call or text you with work concerns, I found cruising to be very beneficial in that you are forcing yourself to disconnect and actually take a break. I have found personally that is harder for me to do when I have unlimited access to my cell phone and wifi.