We did a 13-night cruise tour on Holland America and it was awesome! HAL definitely knows how to do Alaska right, so you've selected a wonderful cruise tour.
As for cruise tours, don't listen to all the horror stories. If you book with a reputable independent company, you won't have any problem. We have a contract with Shore Trips and they will proudly tell you in the tens of thousands of bookings, no one has ever missed the ship! We've used them ourselves many times and have had hundreds of our clients use them without any problems whatsoever.
What those horror stories don't say is that 99.9% of the time, people who miss the ship or are late back to the ship are doing their own thing, lose track of time, or get lost. They are not using reputable independent companies.
But Alaska is definitely one of those places you need to do some shore excursions as it is truly a remarkable place to visit.