I've gone on several cruises. Alaska was beautiful and got to see whales. My son was just turned 3 and he was able to pick out the whales faster than the tour guide. It was amazing. The kids club was great for them and the sights were well worth it.
I've also gone on several music cruises. Kiss Kruise, Beach Boys Cruise, Monsters of Rock cruise. They take cruising to a whole other level. Each of them also has ports of call. I like to tour so I always want to see the sights. My husband would prefer to just remain on the ship. These are like going to a 5 day music festival, but your hotel is right there so you don't have to worry about transportation. We enjoy these immensely but they are EXHAUSTING. Monsters of Rock has about 40 bands playing multiple times on multiple venues on the ship.
I also took an Australian/New Zealand cruise last year. That one was tougher. 18 hours by plane to get there. And there were way too many days at sea - we would leave a port and go just sit out at sea until two days later for the next port that would have been easy to land the same day. Lots of down time. Since it wasn't a music cruise, there was a lot less events happening. Still beautiful and my favorite was New Zealand for the Hobbiton set and the Weta workshop. I'd love to go back. I'm still working and I took off nearly 3 weeks to go. But I figure by the time I retire I won't be mobile enough to tour like this.
The funny thing is that the 3 week Australian cruise WITH airfare cost the same as one of the 5 day music cruises. And the ONLY way we've been able to do this is to not take the whole family. My kids are now adults and the last two are finishing college.
One thing I will note is that the excursions are hit or miss. They can be very deceptive in their descriptions. Some were great, some were a waste. I'd love to retire and cruise frequently but I figure we will only be able to do this once a year at most. I'd love to do a European cruise but I doubt my husband would want that.