Went here a few days ago and of course it turned out to be the hottest day of the year. I was somewhat disappointed in the lack of animal exhibits (compared to Cleveland Zoo anyway) but their Aquarium was fantastic. They have two different play areas for kids which was a good place to let them play while my wife and I rested. The admission was $12 for adults, $10 for kids 2yrs-13yrs and under two were free. Not exactly cheap but tolerable. I highly recommend bringing your own beverages because you will pay through the nose at the vender's/machines ($2.50 for bottled water/pop).
Another downside was that the tram was an extra $2 per person to use where at Cleveland it is included in the admission price. They also had a small train ride for an extra $1 per person of which my 6 yr old son said " This train ride is a rip off."
Overall experience was pleasant but I will probably continue to visit the Cleveland Zoo rather than return to Pittsburgh.