The Calgary Zoo is a great place to visit. The exhibits are awesome, the staff are friendly, and the animals are well cared for. If you have an opportunity to do a behind the scenes, I highly suggest it. Also, talking to the dosents is a great way to learn more about the animals, our zoo, and how ecosystems work in general.
But more than that, it's the perfect location for an event like a wedding. My partner and I held our reception at the Calgary Zoo five years ago, and in recently looking at the pictures, there's no doubt that it is a wonderful choice for a wedding.
Zoo admission is included in the price for each of your guests. This meant that our guests had something to do in between the ceremony and the reception. Additionally, it made for a beautiful setting to take 'summery' photos in the middle of winter. Furthermore, the zoo staff were pleasant, easy to work with, and easy to discuss expectation with and the like.
There are few drawbacks to the zoo. While I remember enjoying the food, my partner did not. Also, if I'm honest, it wasn't particularly memorable to me, and as the bride, in a complete and total whirlwind, I'm not sure I would've noticed the food anyways--I don't really remember eating (although there are some pictures to the contrary).
I highly recommend the zoo as a reception location.