I've been to the Field many times and it never ceases to disappoint. Expect to spend at minimum four hours here to attempt to do it justice. Even then, try to take advantage of the additional hours of admission if they are available.
We bought our tickets ahead of time and that saved us a bunch of time. Just show your phone, they scan it, and on you go. We entered on the ground floor which is far faster, given the line I saw later in the day in the main hall. Masks are required for entry and throughout your stay. You don't have to show your vaccine card (although I hear that will be changing soon). I didn't eat in the cafe on the main floor but the ground floor has bending machines and tables if you need to refuel quick. They didn't check your bags so the snacks I brought in saved us money (which I in turn spent at the gift shop so it all worked out).
Depending on when you arrive, start at the main hall because that section will fill up fast. Go to the third floor and work your way down. The dinosaur exhibit should be your starting point as that is where Sue and the other iconic displays are located. I won't tell you to skip exhibits as I don't want to presume to know what you're interested in. They're all well done. My only knock is that some of them appear rather dated, specifically the reptile area on the main floor. Granted, some of the animals were conserved decades ago and you can't beat the scope of the collection (you want birds, there is darn near every bird known to earth and some that aren't anymore) but when you look at the exhibits dedicated to early earth species or Pacific cultures (which definitely warrants you going through for no other reason than to see a state of the art exhibit) and compare them to the older ones that haven't been updated in a few years, it's pretty clear.
There are sections for every interest. History people will like the Egyptian section. Science people will like the pop up displays in and around the main floor. Those into other cultures will love the Pacific and Native American sections. You just have to be prepared for a long day. Do your research before hand and come up with a plan. Some of the exhibit flow patterns can leave you double backing and/or missing sections which can make you tired and frustrated. If you know where you want to go, however, you can streamline the process and maximize your time.
It's hard to say this Museum is the best in Chicago but for me, this is a must see whenever I am in town.