My answer: Yes, you should consider a Disney cruise.
The reason for my answer is because my wife and I are both 33, have been married for almost nine years, have no kids and we had a wonderful time on the two Disney cruises that we took. In fact, we both agree that they were the best vacations we have ever taken. We went on a 4-night cruise last September and a 3-night cruise in February. You can see our trip report and photos
here. My buddy Monorail has pictures of his 7-night Eastern cruise that he took in June posted
here
I understand your fear, because we had the same concerns before our first cruise. We thought the ship would be full of kids bouncing off the walls and we would be overwhelmed with children all around. But, Disney does a wonderful job of keeping the kids entertained and out of the way, and there's plenty of adults only areas on the ship: one whole pool, the spa, the Cove coffee bar (on the Magic) and Palo, the best restaurant on the ship. The pool, spa and the Cove are all located on deck 9 forward, so that whole area of the ship is pretty peaceful. There's also the "entertainment district" on deck 3 forward that is made up of a dance club, a sports bar and a piano lounge.
Unfortunately, one of the best features that won't be available if you're considering the west coast trips is Castaway Cay, with Serenity Bay Beach which is an adults only beach that is paradise on earth. It is so quiet and beautiful, it makes the cruise completely worth every penny in my opinion.
I haven't been on any other cruise line, so I can't compare. No, there's no casino or gambling, but there is a bingo game nightly.
Some disclaimers: My wife and I are huge Disney fans, so we enjoyed the Disney brand of entertainment on the cruise. Yes, there are many families with children, and there's no way to completely avoid them. But, we had a great time on both cruises and weren't bothered by children either time.
Hope this helps! Good luck with your planning!