I"ve lived here for a decade now. Here are some of my tips.
Museums:
Field Museum is better to visit than Museum of Science and Industry (and easier to get to), but the Shedd Aquarium and Art Institute are just as impressive. I think the Art Institute is the #1 American art museum in terms of American paintings and overall well rounded collection. I've been to the Met in NYC twice now and I don't see how it's more impressive. The MCA is good too if you prefer modern art. Millenium Park is a really cool place to check out for free near the Art Institute as well.
Tall Buildings:
Especially if you are 21 skip Sears (Willis) Tower and buy a drink at the Signature Lounge on top of the Hancock building. It's cheaper, still up high as hell with an equal or better view, you get a drink instead of just a ticket and it's near tons of other shopping and restaurant where Sears Tower is in the business district.
Food/shopping:
I don't blame anybody for trying deep dish pizza (Gino's East, Lou Malnati's) in Chicago but the Chicago style hot dogs, polish sausage and Italian beef sandwiches are incredible. There are a few Portillo's and Al's Italian Beef around town, either will do, and probably a dozen other great places you could find. There's good shopping near Hancock building in Water Tower place and it has an awesome high quality foodcourt for lunch called "Foodlife". There are so many nice to upscale restaurants, too many to chose, Yelp would probably help you as much as me or anybody else.
Nightlife:
The most obvious choices are the bars and clubs on Rush Street (Viagra Triangle) or Wrigleyville. But if you want to go somewhere a little less obvious with more of an artsy/rock type crowd Wicker Park neighborhood is really lively and vibrant almost every night. Start at the threeway intersection of Milwaukee/North/Damen and you'll see lots of bars, restaurants and music clubs in several directions. There's a blue line stop right there too.
Loved the Art Museum, you could spend a day there.