Once they put the lights up for the holidays, the zoo will be great. I was there a month or so ago, and they are doing a big expansion so lots of the zoo is fenced-off. So after that is finished, I'm looking forward to going back.
It's a good zoo, especially for little kids. No so huge that it takes days to explore but big enough to be enjoyable. The thing I like the most is the staff and caretakers. If they are out and tending to the animals, they all take time to explain what they are doing and answer questions, even when there's not a scheduled exhibit. For sure hit the Tropical Discovery and Primate Panorama; if you make it to those 2 exhibits, you've seen the whole zoo in transit.
The Asian tropics construction does short of make it difficult to get around some of the areas but that will be done in 2012 and the plans look amazing.
Anytime of year is a good time for the zoo. We were there just at the zoo last weekend - the weather was actually great and there were no crowds since everyone is in Xmas mode.
The zoo built a parking garage 8 years ago that reaches at least 4 levels down so there's always parking.
I haven't been to many zoos so I don't have much to compare it to but I think its great. My relatives from out-of-state love it and stretched their visit over two days this last summer so that they wouldn't feel rushed with their toddler.