I made it almost through page 4 before Vart mentioned Iowa. I've traveled through Iowa many times and failed to find anything of interest, although the people seem to be nice.
I've traveled less through Illinois but suspect it's worse than Iowa, and from what I saw in Ohio I'd add that state to the list. Indiana might have made the list except I did once travel through the southern part of the state and went through a very nice, hilly area that reminded me of where I live.
The Plains States can be a chore if you're on a timetable to get somewhere but if you are at leisure the stark scenery and isolation has a beauty of its own. I remember many nights driving when I charted my course just by looking at the lights of the towns distant. Once driving through Kansas during late springtime on I-70 I had to pull over on the shoulder to relieve myself. It was close to sunset, driving West. I walked to the back of the car and the setting sun bathed the surrounding grasslands with a wondrous glow, and I think I could see 100 miles to the East with the highway oh-so-gradually sloping downward. It was an experience I've remembered since.