My large family group (six adults, four kids ages 8-11) did Atlantis Aquaventure in July. For us it was worth it. The grounds are gorgeous. We LOVED the Currents Rapid River. Best water "ride" any of us had ever done. The slides were fun, too, but nothing compared to the Rapid River. (And, you can just hop in the Rapid River -- no lines!)
I don't know that I'd pony up the money to do Atlantis again, but we all loved having the experience once.