I visited Chicago for the first time twice this past year. My favorite things were the Upton's everywhere, pizza from Dimo's (although that area was horrifying) http://www.dimospizza.com/
, brunch at Handlebar and shopping with a glass of wine at Whole Foods in Lincoln Park. Native Foods is worth a visit, too, if you haven't been to one elsewhere before. I wasn't that into my visits at Chicago Diner but I'm figuring I just haven't ordered the right thing yet....
The public transit was pretty great.
ETA: and tacos at La Cocina! Way better (and definitely vegan seitan vs. the is it really vegan? faux meats at Quesadilla).
That's my two cents from a Chicago tourist.