We went to the Zoo recently and it was rather disappointing. There is a lot of construction going on (which may or may not be completed due to the budget) Not a lot of large animals. The Komodo Dragon is pretty cool though
There is no admission fee but you have to pay for parking so take the metro if possible. Wear comfortable shoes as there is a lot of walking and most of it up hill.
If you are truly interested in visiting good zoos, you will have to go to other states I am afraid. But if you are looking to kill some hours for free, do the zoo! but be prepared to be underwhelmed. The kids will like the kid zone in the zoo, but will probably not like all the walking between exhibits.
Maybe in 2012 when the construction is finished it will be better.....depending on the budget.