I'd rather explore different sights and cultures rather than just do things i can do at home but if everyone was the same then the world would be a boring place :)
We took a transatlantic cruise in January this year. I'd never cruised before. Met a chap at breakfast one day who made the comment that "only a boring person would find a cruise boring". 12 days at sea? Depends on the individual I guess, but there's plenty to keep occupied. Gym, shows, talks, pools, activity groups - easy to be bored if you let yourself be bored. Plenty to keep entertained otherwise.
Double the cruise cost for a single person. You can get cheaper flights from Norweigian if you are prepared to travel to Oslo or Copenhagen first for a one way flight to Fort Lauderdale. Probably come out as £300 per flight.
Peace, quiet and fresh air in a smart floating hotel with food and drink laid on - a nice way to get away from it all, and, if you have the time, a far more civilised way to travel than post 9/11 economy class in the air, with no sunburnt sangria louts in sight!
12 days at seas seems a bit dull. I can understand cruises that take in cities and/or islands but can't really see the appeal in this.