To avoid sounding like a broken record, I'll make my review brief.
I hadn't been here in about 7 years and barely recognized the place. My partner and I visited on an overcast weekday morning, which was an excellent idea - the zoo is calm and not overrun with visitors, and the animals were not hiding from the sun's rays. It's certainly an expansive (and expensive) zoo - much larger than ours in Nova Scotia - but its layout is pretty awkward and lacks flow. The themed sanctuary buildings are pretty nice features, but the rest of the displays are lackluster. Ensure that you wear comfy shoes and clothing and keep hydrated.
Worth the visit if you're in the area.