I've been to Chicago, Illinois twice. They were both during changeovers on international flights to Asia. If you have ever been to Chicago's O'Hare airport you will know how easy it is to get delayed for many hours. The airport is the closest thing to chaos I have ever experienced. I'd gladly pay a little extra to avoid this place during future travels.
Essentially my "Illinois experience" is limited to the Chicago O'Hare restaurants, terminals and the U.S. Customs Service there. Not exactly the best experience in the world, but not enough to condemn the entire state either. As for Chicago I will say this: It's the first place I've ever been to where people on the subway were actually ruder (by a wide margin) than people in New York.