I went a couple weeks ago too and I have to say I was really disappointed with the freshwater collection. I don't know what happened, but I went through twice and I didn't see ANY pacu, arapaimas, arowanas, rays or anything! Such a bummer! The only freshwater I saw was the super-stocked cichlid tank, the gar tank, catfish from below, amazon with tetras, angels and discus. Then they had some otters, the electric eels, some elephant nose fish and maybe a few others but no real MONSTERS.
I went to the ripley's aquarium in Tennessee back in January and they had some nice freshwater fish. They had one big tank with a couple 24"-36" Pacu, a big arapaima and some large oscars/other cichlids. I mean they didn't even have any large silver dollars or rays or anything at the Georgia aquarium...
I was very impressed with the large reef display at the Georgia Aquarium though. It had a really cool wave effect that I liked. The other large marine displays were impressive, but seemed to be lacking too. There were many large groupers and other shoals of "plain" fish. I think the balugas and whale sharks are the highlights of the place in my opinion.