We did Alaska on RCCL. We did one official excursion, to Jewell Gardens for tea in Skagway. (perfect and beautiful)
We wandered Juneau, getting on the blue bus for the glacier, went to a bookstore, bought a souvenir at the tavern, found a great Mexican restaurant in some "back" streets.
Got off the ship in Ketchikan and within the hour were back on board.
I can think of nothing we would change in the future.
To not get off the ship in Vancouver, though, hurts my heart and brain. Vancouver is an incredible, wonderful, gorgeous city and deserves to be seen and walked in. If only for a crepe from Cafe Crepe or an interesting hot dog (or veggie dog!) from JapaDog. You have to walk a little bit for those (though there are locations for both in many places) so it kills two birds with one stone. (poor birds!)
We just did the Bahamas 3night cruise, and if we went to Nassau again we would do an excursion. We TRIED to do the walking tour to the Staircase, etc, but the streets, lack of sidewalks, cars nearly on the road, lack of streetsigns, etc, made us too nervous. It was just the 3 of us. My cousins' friends did the 4 day the following week and had a GREAT time doing that walk. In a group of 20. Makes a difference, and I think that some people had been on the walk before.