It's common knowledge that Disney Dreams is the show not to miss. They even have an afternoon matinee of it presumably to handle crowds and so the little ones have a shot at staying awake through it. If you have kids who love the characters or an adult who loves disney, you'll love this one.
As far as the other shows, I enjoyed most of them. We saw the "welcome aboard variety show" and thought it was great. It featured some singing and dancing and two of the nighttime cabaret acts (one of whom we missed, disappointingly enough, and the other whom we saw, and he was great in his longer show).
The next show is Hercules the Muse-ica. My husand really didn't want to go to it but I did. Neither of us thought the movie was so great but I thought a live show would be fun. I still haven't heard the end of it... it was terrible and impossible to follow. OH well. Still, I'm sure some people like it so you might want to give it a try and see for yourself, but if I had to miss one this would be it.
The Morty the Magician show was also extremely entertaining. It combines some classic magic tricks with some neat stage effects and a really cute storyline.
Who wants to be a mouseketeer is also somewhat entertaining, but I would probably skip it next time. The fact that you have a chance of getting on the show and winning some money kept us there but we MUCH prefer the MGM version where you can really play along and it's your skill and speed in answering the questions that gets you in the hotseat and not luck. If I had to miss two this would be the second to go.
There's also a farewell variety show which I assume was similar to the welcome aboard one and I'm sorry to have missed because we were packing.
There was also a showing on our cruise of Monsters, Inc. Since we had already seen it in the theaters, we took this opportunity to enjoy more of the ship.
Hope that helps!
Lisa