My DD14 insists on Coral Reef as her must do each trip. She likes the food but really enjoys the atmosphere more than anything. Since it's just the two of us, we are pretty much guaranteed a seat down by the tanks which she loves.
My must do is Boma. We've gone for dinner both of our trips thus far and again in May 2011 however, I'm adding breakfast also to the next trip since I've heard so many good things.
While we didn't get a good experience from Ohana our first trip, we really enjoyed it the second time around when we gave it another shot. We're going again.
For signature dining, Narcoosee's is now our must do even though we're adding on several others this trip (Cali Grill, Citrico's, Luau and debating on a couple others) DD LOVED LOVED LOVED the whole main lobster. We watched Wishes from the deck and it was spectacular. The server here was outstanding and just gave us a really nice night, including the special Cinderella's slipper I ordered for her as a surprise. The server never gave up the surprise and brought it out at just the right moment and it was just a wonderful night for us.