Alaska is one of few places I've traveled where I would say it is essential to do excursions(though you need not go through the cruiseline). Views off the ship are amazing but the ports are small and have little to offer aside from shopping or stretch your legs after being stuck on the ship a few days.
Depending what time of the season you go you can see whales off the ship, seals, even maybe a bear but it's luck of the draw. Unless you spend the whole day watching off the bow of the ship it's way easier to go on an excursion to where the animals live(and see 200 seals) instead of hoping to catch one pass by.
Also recommend Celebrity cruiseline as they tend to have less kids, better staff and higher quality food. They might cost 100-200 more per week but it's worth it. For example I just spent 3 weeks on the NCL Epic and the best way to describe the experience is death by a thousand cuts. Nothing so bad it ruined the trip but everything had issues from rude staff, to cold food, to ordering drinks and they never came. Celebrity is like an ipad it just works smoothly out of the box.