Worth it as a tourist.
Let's face it as a tourist there are the heavily marketed spots and the hidden gems. The CN Tower is an international attraction and situated right downtown Toronto.
I personally like the Hancock Building in Chicago better but the CN Tower is great to add to the list of things you have done!
There are two parts you can see, the main area of the tower and you can pay to go higher. The security is a bit of a hassle getting in, but I would rather it be more secure then not.
The views atop are beautiful, mind you I was there in the winter and I am sure in teh summer you can get a better view of Toronto Islands.
Make the CN Tower part of your Toronto tourism stops!