Well I must start buy saying that this is clearly better suited for a summer visit.
I have come here both in summer and recently came in winter. Although during the winter month this place is not as crowed the line ups are not as long so you really do get to enjoy the visit a little more. There is of course a lot of waling to do, a lot! There is so much to see, my favorite place is the Tundra and the Canadian plains (I may be a little biased). I was surprised to see all the Asia animals out, I did not think they would like the cold but it seems that they do especially the two hump camels.
Over the last 2 years the main attraction has been of course the newest addition to the Toronto Zoo, a pair of Pandas. I had the chance to see them and they were everything I expected, they reminded me so much of PO from Kung Fu Panda :)
Over all I had a great time here and I will be back for another visit in the summer time of course when I will enjoy the walking a lot more!