This is a great sized zoo with lots to see. We were there for about 4 hours and were able to spend ample time everywhere and see nearly everything. Yes, there are some animals that are off exhibit and yes, the trolly seats could use some updating, but it is worth a trip out.
The rainforest is included in your ticket, but it has a separate entrance from the zoo (right by the ticket booth). Be sure to check out the river around the porcupine exhibit. The display will suddenly rain and then mist. It is pretty neat to see.
It seemed like the exhibits are set up so that you can get very close to the animals. The zoos we are familiar with have a much larger separation between guests and animals.
Some animal highlights were the lions (we got to hear them roar), the elephants (several views that you can see them from and a few that get rather close up), the grizzly bears (they get so close and one seemed to be smiling), the tiger (he was sitting on the overpass, so we were just under him), the sloth (he was moving pretty fast and was teasing another one in a tub), and a koala (wide awake and looking all around).
One review I read said to park at the northern parking lot, but that gate was not open when we arrived. We had to park the farthest out at the main gate when we arrived at around 12:30 on a Tuesday. if we had driven around the other lots more, I'm sure a closer space would have opened up for us. Maybe the other lot/gate is open on the weekends.
The Australian playground is really neat. Be sure to stop there if you've got a youngin.
You can take food and drinks in.
We'd recommend taking the trolley up to the primate/aquatic building (I've never seen this combo in a zoo before) and then back down afterwards). It was a nice ride and gives your feet a bit of a rest.
The lantern display is lovely even in the daytime. We left close to closing and things were starting to be lit up and they were very pretty.
The only negative of the day for us was the vast amount of information on litter, deforestation, and pollution. My youngest is very environmentally conscious and it was distressing for him to see information about it at every turn. Maybe including some success stories (there was a wolf video we saw inside that building that talked about some successful attempts at building the wolf community in the west) and more information on how to become active for kids (besides donating money) would provide more balance for those kids that are very affected by the destruction.