diner suggestion
As with all the above, Chicago is well worth the visit. There are many great places to see and things to do. A mind boggling choice of restaurants and bars.
One suggestion for some non formal eating which I really enjoyed is a classic American diner called Ed Debevic's. It is a retro 50's/60's style diner with a fantastic array of kitchy memorabilia decorating the place, but it is great fun. They do well what a lot of imitation diner style places in Ireland/UK try to do but fail. It is great for kids as there is so much going on. The staff are dressed in 50's attire and are famous for insulting the customers (done in a funny endearing sort of way). 'Whaddya want?', 'Don't got none' and 'You need a haircut' sort of stuff.
The food is good and tasty, but not spectacular and not the cheapest you will find. The milkshakes are massive and excellent.
It is very popular and so the downside is you often have to queue for a table. The place won't appeal to everyone, but really is a fun place to eat.