My husband and I have done 5 cruises, 4 to the Carribean and 1 to Alaska. Alaska has a lot of offer but the weather can make a big difference. We hit a really good week and enjoyed the side trips. Try out the Jeep /canoe excursion and the wildlife excursion. The narrow guage train ride is also worth the price as you get the best view of the scenery. If you something really challenging, hike the Chilicoot trail and then cruise!
My favourite Carribean trips were the "Saint" tour, doing St. Maarten, St. Thomas, St. Barts etc. I also really enjoyed our last cruise to Belize, Costa Rica and Panama. I would avoid the Mexico, Jamaica stops but did enjoy Grand Cayman.
That's my two cents worth!