First and foremost, I enjoyed the trip. I do wish I'd taken the Southbound trip though, and here's why: Northbound trip goes to Glacier Bay and College Fjord, while Southbound trip goes to Hubbard Glacier and Glacier Bay. My opinion: College Fjord is not worth going on a cruise ship. The scenery is sort of "similar" to Glacier Bay, and I now think Hubbard Glacier would have been a much better choice. In fact, College Fjord is so close to Whittier, it might be possible for you to take a morning trip out of Whittier to College Fjord before you board the Southbound trip.
Diamond Princess Ship: I don't know if its just the specific trip or if its all Princess Cruises,it seems like the tourists onboard is an older crowd then perhaps RCL. There's not many people go dancing in the clubs every night, while my parents said a lot of folks packs the clubs and lounges at night during their last Alaska trip on RCL. Overall the Ship is very comfortable and I enjoyed the ship a lot.
Inside Cabin: The cabin is not big, but comfortable. I kind of wish the closet area is larger, but its manageable.
Food: very good in general. A bit salty for my liking. For East Asian travelers, I would recommend go to the "Pacific Moon" room for dinner, as they have a stir-fry noodle dish (not on menu) that is very good and does a good job relieving you of Chinese food cravings. I never tried the Grill by the pool, but the pizzeria is very good as well. For breakfast, there are rice porridge, for those Asian travelers that is not used to American breakfast.
Entertainment: the song and dance shows at the Princess Theater are terrible in general. The various musicians in the lounges are pretty good. The string quartet is not very good.
Childcare: my 3 year old love the little kids program onboard. He made new friends, and he couldn't wait to go to the Pelican Room everyday to go play with them. The childcare folks are kind, fun, helpful, and accommodating.