Our family of four (kids age 10 and 15) just finished the Tracy Arm Inside Passage itinerary on the Grand Princess. We booked two cabins, a balcony and an inside cabin across from it on the Caribe deck. A balcony cabin is an absolute must when going to Alaska. Both cabins were decent and the beds are very comfortable. The inside cabin seemed to be showing less wear than the balcony cabin - I'm sure those are the most popular. We saw seals, whales, and bald eagles from our balcony cabin that we might have missed otherwise.
The ship does have some wear but overall was nice. The buffet food was decent and there is always plenty of it, although very crowded at times. If you go during off times, you can find a nice spot at the window and get great scenery on the buffet/deck 14. The food in the main dining room was decent as well, and a little less chaotic than the buffet. If you want to spend a little extra at The Crowne Grill and Sabatini's you will get a noticeable improvement in food quality and atmosphere.
We weren't really interested in the entertainment much, but we did like the magician who has two different shows and we saw both of those - he was very good. The kids like the golf and ping pong tournaments and the MUTS are a lot of fun if not too cold and windy. There is an indoor pool (Disney does not have an indoor pool on the Wonder) which is very nice and bigger than most. The ship's naturalist (Mark Harris) narrates through several key points of interest (Tracy Arm, etc.) and we really enjoyed listening to his commentary.