The lions are amazing and beautiful. We got our tix at the box office of Luxor as part of a 3 for $57 deal. Good value as we were able to check out Bodies Exhibit as well as the aquarium Shark Reef experience at Mandalay Bay. There is a great underwater viewing area of the 6-8 dolphins they have and it's wonderful to see them play with each other under water. Perfect for kids.
I would recommend devoting at least two hours to this walk through of exhibits to fully take it all in. We took the tour at 3 o'clock on a Wednesday in January. There was about 100 people there at the time along with us and it made for easy walking along side the lions and tigers.