Our library held weekly raffles for free books during the summer reading program, and Levynn (who also won another week) and Lincoln each won the same week that the library was tossing in free passes to the Brookfield Zoo as part of the prize. They gave us four passes, and we didn't wait long to use them since that's one of the few places we haven't been.
The zoo, just two blocks from a Metra stop in the western suburb of Brookfield, is beloved. And once there, we could see some reasons for that.
It's like part zoo (with many of the same animals as Lincoln Park Zoo), part aquarium (with a large indoor aquatic exhibit), part nature museum (with a butterfly sanctuary, like at the Peggy Notebaert Nature Museum) - which is great for suburbanites, but not so special for us city-zens.

It also has more lush environments, like this polar bear exhibit, than Lincoln Park Zoo.
And there are really big animals:

Like this bear,

this gator,

this hippo,

and this kangaroo. Uh, wait a minute...

(We also stumbled on this itty bitty baby bird in a patch of grass where we were resting. We watched it meander onto the walkway, where a passing zoo worker saw it. And she knew the bird!)
The thing is, this zoo doesn't seem to have any more animals than Lincoln Park Zoo, yet it feels twice as big as you're walking around it. There are long stretches where there are as many places to spend money as there are animals. And, speaking of money, this zoo has multiple levels of admission charges; Lincoln Park Zoo is entirely free, parking notwithstanding.
So we took a vote afterward, and Lincoln Park Zoo won 3-1.
But Brookfield Zoo gave us a full day's adventure, and we're grateful for that.