I have to say I did many Caribbean cruises also so you are not alone. I had a friend who had done Alaska and I wondered why he loved Alaska. I only went because I had a free trip as "I would never pay to go to Alaska". Well - Alaska has sold me and I will pick Alaska over the Caribbean time over time. Honestly I can't remember the last time I was in the Caribbean as I have been cruising elsewhere including Alaska.
My first trip to Alaska for in 2002.
Alaska has changed a lot. Glaciers have retreated quite a bit. Also, the ports now seem over run as the cruise ships coming now are much larger and more ships are coming. Thus, I encourage you to get out of the port towns.
Have fun planning. Very few people do not love Alaska. The good thing is that you have plenty of time to plan. Alaska also attracts a lot of people who are not cruisers but want to see Alaska so there are plenty of new cruisers on the ships also.