Years ago during a previous visit to Mandalay Bay, I had tried to get in to see the Shark Reef Aquarium, but the wait had been an hour or more long so I skipped it. For this visit, there was no wait whatsoever and we went right in.
Having visited several Aquariums in my day, I'd say this one is on par with just about any you might see. The Stingray "Touching" pond is a nice touch though, and is probably an extra bonus for the kids
Overall, it didn't blow me away, but neither did it disappoint me. If you are in the mood for an Aquarium, you will likely have an enjoyable time.