No one should go to Chicago with out going to the John Hancock Observation Deck! The city is fabulous to look at and this is the spot.
The observation deck gives you a great view of the city and gold coast. Going up later in the afternoon allows both a daytime and dusk view if you have the time. Watching the sun go down and lights come on in a city is always interesting.
It was a clear night so we had great views and the night lights added to the views. If you are a serious photographer though don't expect great photos as the lighting inside the building means you get a lot of shadow. I know it would be hard to change that as folks need to see where they are going. We did the Tilt experience as well. I am glad I did it as I do have a fear of heights, but whilst it is moving look straight ahead. Look down when it is still.