Definitely something to experience when you come to Toronto. Beautiful expansive views of the city by day or by night and plenty of opportunities to take pictures.
Splurge and get the glass floor package if you can, because this is something you probably won't experience anywhere else. When you step on the glass floor, you have an unimpeded view of the city 147 floors below where you are standing. Based on what I read on a wall, this glass floor is so strongly reinforced that it can hold the weight of 14 hippos at one time, now that's impressive.
Go and enjoy.