My Fiance, George and I visit the Detroit Zoo about once a week. We LOVE the Detroit Zoo and, especially, Trio and Buster (the racehorses who were rescued and reside at the Detroit Zoo). The only change I would request is the VERY high prices. (A can of pop or a bottle of water is a whopping $3! WOW).
The staff is extremely friendly and I would definitely recommend purchasing the annual pass (as it would save you tons of $ if you visit the Zoo often as we do).