The Field Museum was on our must-see list of places to visit in Chicago, and we were not disappointed. It was a highlight to see "Sue" of course, but so many other fantastic exhibits! Leave enough time (2-3 hours) to see everything comfortably without having to sprint thru each. There are enough different exhibits to appeal to everyone in your group. Great gift store -- cool stuff, and the museum cafe was tasty. The building itself is vast, and just a lovely exterior and grounds. Walk around it so you can see the landscaping and cool public art. You can take the train to get there, or if you are doing one of the hop on/hop off buses, they make a stop there.
Admission is not cheap, so plan in advance either using CityPass or if it's cheaper to buy tickets online in advance. Research your options. We have a membership to the science museum in our city and found out that they had a reciprocal admission agreement with The Field so we did not have to pay admission just had to show our member card. However, we could not see the special exhibitions, FYI. We saved a lot of money so it's worth taking the time to do research before your trip. This is a wonderful museum and worth the time to visit on your trip to Chicago.