I'm finished with work for the day, so…
1. People. People in Chicago are genuinely nicer than any other place I've lived. I've lived in 27 different places and most of them are in the South where people are supposed to be pleasant and hospitable, and it's not even close. Chicagoans are nicer. I also like the diversity of people you meet in the city. As a bonus—and I have no data to back this up—the woman seem to be taller. I like tall women.
2. Food. The collection of high-end places in Chicago is as good as any other city in the country. The diversity of ethnic restaurants is as good as any other city in the country. Italian beef is amazing. The hot dogs are amazing. I never cared for pizza in Chicago, but I've developed a dairy allergy, so that doesn't really matter anymore.
Obviously, food also includes groceries. I don't like most supermarkets. Between the farmer's markets, butcher's shops and specialty shops (Old Town Oil, The Spice House, etc.), I rarely had to go to a supermarket. The only problem I ever had was buying dry foods (grains, beans, nuts, etc.) in bulk. I do that to cut down on waste, and the only real option I ever had was the grocery store. But even then, there's plenty of places like Whole Foods around. It's not ideal, but at least it's an option.
3. Architecture. Between the collection of Wright Houses (and I'm counting Oak Park because it's a train ride away), the Mies buildings, the Louis Sullivan (and all of his followers) buildings and every other significant building in the city, Chicago has the best collection of architecture in the country.
4. Public Transportation, Density and City Planning. I'll combine these three because they all work together. Chicago is really walkable. Other people have a problem with the traffic. I never had a problem with it, because I didn't drive. Problem solved. The CTA could obviously be more efficient, but Chicago still has a better system than all but a few cities in the country.
5. Parks and Museums. Between the parks, the Art Institute, the Field Museum, The Museum of Science and Industry, the Adler, the Shedd and all of the smaller museums, there's a lot to do. I'm also a cheapskate, and there are plenty of free days at the museums.
6. Neighborhoods. I like that I can move from Uptown to Pilsen and feel like I'm living in a totally different city. I also like having neighborhood corner stores, neighborhood coffee shops and neighborhood bars.
7. Bars and Live Music. It may not have the best collection of bars I've ever been around (I'd probably go with New Orleans for that one, especially per capita), but it's pretty close. Again, the diversity is the selling point. The neighborhood bars are my favorite, but I love places like The Green Mill. The music scene is probably not as good as it should be considering the size of the city, but there's still a lot of good local bands. And of course, almost every national touring band is going to make it to the city at some point. The free concerts are great in the Summer.
8. Sports. I love the Bears, Bulls and Blackhawks. Even if I'm not attending a game live, it's nice to know that the game will be on TV. I also like watching games at bars with likeminded fans. I don't really follow baseball anymore, but I like going to The Cell and Wrigley. All five of the major sports franchises have stayed in the city rather than move to the suburbs. That's a huge selling point for me. Chiago has more major sports franchises within its city limits than anywhere else.
I could make a much longer list, but I think I'll stop here.