A great walk, with superb animals! The animal environments are very clean, and the inhabitants seem very happy with their man made homes.
If you happen to be in Phoenix during December or early January, make it a point to go check out the Zoo Lights. Weather will be much cooler then the summer months, and the lighting displays are really inventive and appealing.
Overall, this zoo is one of the better ones I've been to, and doesn't disappoint on any level.