We just ate at Coral Reef last week using the Dining Plan. Keep in mind that with the dining plan, you get an appetizer (shrimp cocktail, salad, etc) entree and desert so while the portions may not be huge, you won't leave hungry. Our meals took a while to come out of the kitchen, but we had a party of eight so that may have had something to do with it. Our waitress was very attentative though. It wasn't the best food that I've had, but it wasn't horrible either.
Our ADR was for 5pm. We got to see two sets of dive teams exploring the "seas" which was very cool. At one point one of the divers was interacting with some of the diners, when two sea turtles came along "interacting" with each other. The diver didn't see them at first but saw that that side of the restaurant was laughing at him. He turned around to see what was happening and quickly covered his eyes. The diver went away for a minute and came back with a sign saying "Privacy Please". He then went and got a black cape to provide a little more privacy.
A quick note about the cost of the dining plan. We had two adults and one child in our party which cost us about $85 per day for a snack, counter service meal and table service meal. Our Coral Reef meal alone "cost" $180