I spent a couple of days in Chicago in September 2003,
and I must say I liked it.
It's a real city, something that cannot be said about all American cities.
The capital of modern architecture, they said on an architectural
cruise on Chicago river (recommended). In addition to the cruise,
I visited Sears Tower (of course), Navy Pier (a tourist trap),
Museum of Science and Industry (the coal mine was nice) and
The Art Institute of Chicago (several famous paintings and tons of
other artwork).
I ate the famous Chicago-style pizza (not that good) and famous
Chicago-style hot dogs (not that special).
The public transportation is good, there is even rapid transit service
from both airports to the downtown.