My family and I went on an Alaskan cruise last week.  It was my first cruise.  I liked it.  There is a lot you can do on a ship during a cruise.  There is a casino, Broadway-style shows, art auctions, night clubs, various games (like trivia), and much more.  I didn't do most of it, yet I wasn't bored.  Just sitting on the balcony reading a book and watching the islands pass by was quite enjoyable.  The food was amazing.  Every evening is a five-course meal.  The staff is amazingly helpful.  Alaska is has a beautiful coastline (when the fog isn't in the way).  Our cruise went to the Inside Passage, Juneau, Skagway, and Ketchican.  I liked Skagway the best even though it is the smallest.  It is an interesting town to explore.

I can now see why there are so many special interest cruises.  There is a lot of time hanging around--especially in the evenings--that it would be really cool to walk by a lounge and be able to join in a conversation on something of interest to you. 

If you've never taken a cruise, consider it.  It's definitely worth doing at least once.