My husband and I did the HA cruise last year that was one way Vancouver to Seward. It was fantastic and we loved every minute of it! I must caution you, however, that HA is know for its high service and beautiful ships. It is not the FUN ship and there was not a lot for kids to do. They did have a kids club, but the week we were there, there was only a handful of children. Luckily, my husband and I were content to sit on the deck, read books and watch the beautiful scenery, since our kids were at home, but if the weather had been foggy and cold (which I guess it normally is) we would have been looking for things to do. We are in our early 30s. There was only one other couple on our ship our age and they were with a set of in-laws. Everyone at our table for dinner was over 60.
Would I do it again? Absolutely! Not on Holland America, though. We were on a beautiful ship, but there were almost no activities besides playing cards or working out. No golf, etc. Like I said, we were so happy to just get away we didn't care.
We went June 20-27 and had warm sunny wonderful weather. While on the ship, however, they were telling us they'd never seen it like that for so long. There is one mountain they said they hadn't seen in a year because it is always fogged. I know many people who have done the cruise and they've always had cool, foggy weather, but enjoyed themselves anyway because the views are breathtaking.
My advice: don't worry too much about dressing up, even on "formal" nights, most people wore what I normally wear out to dinner, some much more casual; bring two sets of binoculars (sp?), if there are whales, otters, bears, etc nearby you don't want to be jumping up and down saying, "let me see, let me see!"; bring a windbreaker or waterproof jacket (normal cruise fashion goes out the window for Alaska, warm and casual are in); plan shore excursions in each city; in Juneau, try to climb to the top of Roberts Peak. You take a cool elevator up part of the way. The hike takes a very long time, but the views are amazing. We have pictures of ourselves in t-shirts and shorts (the only ones we saw who had thought to bring them (just in case)) standing on the middle of a glacier. I will caution you, this is Alaska, if you take kids, I would not take this hike. My husband and I turned back just short of the peak because we were scared we weren't properly equipped. The incoming jets were lower than we were. It starts out really easy, and then you get an adrenlin rush to see how far you can go.
PM me if you want to talk more!