I've done Atlantis Beach Day twice (2013 and 2015.) The first time was great! Our guide was great, the beach was clean, the walk was long but it was a nice secluded area (not public beach) for the guests of the resort and other cruise lines. The food was good and near by as was the public restroom. The chairs had nice covers for shade. It was worth it which is why I decided to take my mom in 2015...
It was pretty horrible. The guide left our group when we arrived. People wandered around the lobby of the hotel just waiting. Since I knew the area, mom and I walked to where the beach was in 2013. We come to find out that they changed the beach and now it's a public beach at Atlantis, the food locations changed and were no where near where we were sitting. The beach was dirty...chairs broken. We ended up spending less time on the beach and more time walking around the resort and seeing the aquarium area which I didn't do the first time. We did share our concerns with guest services upon returning to the ship but they simply just said it is not in their control and that was it.
Our table-mates went to Blue Lagoon of the dolphin swim and beach day and LOVED it. They said it was clean and the ride over on the boat was nice. I wish we had done that but at least mom got to check off Atlantis from her bucket list! As of now, were planning on staying on the ship for our cruise in March (maybe just the straw market.)