I had been nervous about this, I'm not affraid of heights, but I do have limits too and when I'm that high I can be hit or miss. This did not bother me at all, I was on and off it a couple times. I found all the tourists here to be friendly and happy to take pictures of each other, and they even took a great picture of me!
The views of the city were really nice, naturally things on the ground were tiny, but it was a great way to see some of the cool architecture in the city.
One thing I've realized is that as much as I love to go to high locations to see cities you get a more intimate feel from a lower high point. The Arc de Triumph gives a great view of the city because it's shorter, you can see the long avenues. But from the Eiffel Tower you can see more of the city. At the Willis Tower you can see the tall buildings and points further away, but you don't get to see the intimate feel of the city. That doesn't mean I didn't like it, Chicago has a good layout for being viewed from 103 floors up, but it is a big picture view, not an intimate view.
If you like to see cities from high up, this is a great place to visit. If you can go early in the morning then I wouldn't bother with the Citypass unless you had already wanted to get one. Going early will not only allow you to skip the line, but it will also be less crowded. Visiting only took me about an hour, including visiting the gift shop on the ground floor when I exited. If you're not intersted in city views like this, then you might want to skip this if you have limited time in the city and concentrate on some of the other offerings of Chicago.