I thought New York was a good shopping city but Chicago has pretty much the same big name shops and they're spaced out. The 900 Shops was probably my favorite space in terms of cleanliness, space and quality of shops.
The best J. Crew is here and their staff are phenomenal. I really liked the Bloomingdales and the Club Monaco here as well.
I found that the selection was much more varied and the quality of shops was better here and on Michigan Avenue than on State Street.
There is also an ATM on the first floor because you will run out of money.