Hocking Hills State Park is a very beautiful natural wonder in Ohio, but the state park campground was ok. The main complaint my group had was with the bathrooms. The women's bathroom near our site had 4 stalls - none of which had doors which would close. They were beautiful big, heavy wooden doors, but each was too big to actually close and lock the door! Fixing this may take 1-2 days work, but someone could easily remove the locks, run the doors through a saw to cut off an inch, stain and seal the exposed wood, and re-attached the locks. Old Man's Cave has a brand new welcome center, but the campground still has bathroom doors that don't close. It doesn't make sense to me.
The only other complaint is that the asphalt parking areas at each site are fairly small and there is no parking provided for extra vehicles. Having a large group with people driving separately makes it difficult as there is one parking spot on a site (if you set up a camper).
Other general notes: Many of the sites have a lot of slope, as you are in the hills, though each appeared to have at least one small flat area. The showers are fairly open, with curtains on each shower and a large curtain separating the shower area from the rest of the bathroom. They have a bench, hangers for towels, and a shelf for soap. The showerheads themselves are very nice and always had warm water! Another newer bathroom we visited (near the pool) had been remodeled recently, but was significantly dirtier than the old one. There was mud and toilet paper all over the floor and it was smelly.
Overall, the campground is in a great location. You can easily hike to Old Man's Cave, Rose Lake, Cedar Falls, and the Devil's Bathtub. Most of these trails lead to other areas 4-5 miles away as well. And being within walking distance of the trails, you don't have to worry about parking (and boy was it crowded this Labor Day weekend).