Falls Park in Sioux Falls is a neat pit stop if you've been driving for a while, but there isn't anything memorable or super unique about Sioux Falls that really screams "stop here." If anything, make a night in Sioux Falls and stay in a good hotel and go eat somewhere; maybe go to the Washington Pavilion as a museum/exhibit kind of thing, go to the falls at night (I dont remember if they are lit up at night or just special occasions).
If you want to make it off the beaten path and you're an art lover -- the Terry Redlin Art Center in Watertown (north east section of the state) is a cool stop. The problem is, it will will take you a significant amount of hours away from your destination because its 3 hours away from I-90.
If staying on I-90 from Sioux Falls, the next "stop" you'll come to is The Corn Palace in Mitchell. It is not worth seeing; but it makes for a stupid/quirky facebook post to show you're literally in BFE. If you need a pee break, its just a short drive in the town -- stop and rest your legs and grab a snack/refuel, cuz you have a long ways to go before your next stop.
4 Hours later, and 50000000000000000000000000 ridiculously stupid, ugly, and mostly religious, billboards later, you'll hit Wall Drug and the scenic pass to go to the Badlands. I would recommend driving through (don't stop) at Wall Drug and making a night at Rapid City. Like Sioux Falls, there isn't anything special about the city, but there are some neat things just to 'see' if you're out and about looking for dinner. Some cool day hikes in the hills of Rapid if that tickles your fancy.
Once well rested, hit the Badlands as early as possible. It gets HOT, regardless of what the weather report says for the day. Bring your sunscreen, shades, and have lots of water if you're gonna hike the longest trail (which I think is 10-15 miles). You can go off trail too, but thats kinda sketch. Watch out for rattlesnakes. Even if you aren't going to hike in the Badlands, they are worth driving through and this should make it on your "must do" list while in South Dakota.
Drive through Custer, stop at the best burger place in the United States (literally) [Black Hills Burger and Bun Co.] and make a drive trip through the Black Hills up to Mt. Rushmore/Crazy Horse/Hill City. They are lame, so its best to tackle them onto something unique that day; I recommend hiking Black Elk Peak, and then back into Rapid City for another night.
Go back into the hills and go through Spearfish Canyon (do more hiking if can fit it in, there are lots); stop at Leone's Creamery for some badass ice cream and sandwiches. If you like gambling you can head up to Deadwood too; but imo Deadwood is really fucking lame and people need to get over the whole "the wild west still lives in Deadwood" mentality because its literally dead of all fun.
Devil's Tower Wyoming. Again, neat to see; low on the "this is exciting" scale
You should have a wonderful time camping in the Badlands. I can't really comment to the Bison, but remember they are big ass animals. Leave them alone, and they'll most likely leave you alone. Also there has never been a documented/reported mountain lion attack/death on a PERSON in the Black Hills; that being said -- they do exist and are seen regularly. Make yourself look big, don't ever turn you're back on them, and if you can -- hike with an external speaker to make noise to scare them away.