Fun for all ages. You walk in to the dolphin area first. This in itself can provide a fair amount of time where you feel entertained without doing anything. Watching dolphins play with balls and chase each other is just naturally relaxing and worth chilling out for a bit when considering the hustle and bustle of everything else in Vegas.
After the dolphin pools is the cat sanctuary. Now the thing to remember is that most of these animals are nocturnal so they just sleep in the day. If I didn't like cats, this place would be a 3 star, as its not very exciting. But still, seeing lions and tigers, leopards, and the like up close really makes you appreciate how mammoth these things are.
Given how quickly $20 can be spent elsewhere in the city, this is worth the stop.