I've been to the zoo a couple of times...once for a regular family trip in the summer and more recently a Christmas Party in the evening.
Calgary is a well maintained zoo. It has a great layout, not too small but not so sprawling that you can't see everything over the course of a few hours. The regular food service is good and fairly priced too which is nice.
Event wise I was very impressed. We had our party at the conservatory and it was both an interesting and amazing venue. The food, a selection of appetizers and other nibbles set up at various food stations, was fantastic. Roast beef on a bun, sushi, fancy desserts - oh my! The staff were friendly and very professional. The washrooms were clean and were maintained throughout the evening. I can honestly say this was one of the best event venues and experiences I have had in Calgary. I wouldn't hesitate to recommend it to others for Christmas parties or weddings.
We were lucky enough to catch a bit of Zoolites too as the party started. How beautiful! There were scores of families taking it in and from what we could see, lots of happy kids.