We went to the Georgia Aquarium yesterday. First off, if you can give yourself two - 3 days in Atlanta. Look into the City Pass - costs $59/adults and $45/children. It includes the aquarium, cnn tour, world of coca-cola, high museum of art, then pick one of zoo or history center AND museum of natural history or botanical gardens. This also lets you right into the aquarium rather than waiting for a specific time to get.
Second, all-in-all, I wasn't very impressed with the aquarium. The whale sharks were pretty cool; but, otherwise, there was nothing else there you couldn't see anywhere else. We live in Wilmington, NC. There is an aquarium in Fort Fisher. Everything that was in that aquarium we saw in the Georgia Aquarium plus the whale sharks. Nothing overwise spectacular. They do have an exhibit with some saltwater fish common in the trade. Trust me, someone will complain about the mandarin fish in a tank without live rock (yes, it was - and there were 2). Otters, penguins, sea lions, and belugas were cool.
There were a lot of people. I understand why they time the tickets. Hundreds of people. Hard to spend any time at any single exhibit. Many parents were pushing people right out of the way so their kids could see.
Overall, it's worth going to see probably once, but not again until the whale sharks get bigger (AND they want to breed them-- that'll be very cool)