I just returned from my cruise a couple days ago.
We did not have a booked excursion to Atlantis. We took a water taxi to get to Paradise Island ($6 roundtrip) and with a short few minute walk, we were at Atlantis. If you don't pay for the full tour, you can still have access to some wonderful aquariums, as well as some of the shops and casinos. I was pretty satisfied from what I was able to see without having to pay for the full tour.