We bought our tickets as part of the three for $57 they are running. It was a good time.
The aquarium isn't particularly big, but that seems pretty common for Vegas; nothing lasts too long. The hall surrounded on all sides by water is an essential aquarium experience that was worth it. Also the touch tank was fun and the Shipwreck room was fun to look at. We spent most of our time there, watching the TV cycling through the numerous species in the tank and then trying to find them all in the tank.
I would go back if I was bringing someone who hadn't been before.