We popped up there for one night on our way to the east coast. We didn't stay long, but the park seemed nice. We were in site 95 I believe which was a pull-through. Site was level. Bathrooms were nice. The park was pretty crowded.
We just finished our second visit to O'Bannon. The first was over Labor Day weekend and the second was over fall break. Labor day was wall to wall people and the this past week was very uncrowded. The sites are a decent size. We camped on the perimeter both times (195 and 197) which back up to the woods. We like the park and it is quiet with lots of good hiking trails. Plan ahead on supplies as there is nothing close to restock. Corydon is 20 minutes away with everything from Walgreens to WalMart. The Falls of the Ohio State park is a nice side trip. The Overlook restaurant in Leavenworth is great place for lunch/dinner with a fantastic view of the Ohio river. The restrooms are clean. Canoeing on Blue River is a short drive and it is a beautiful paddle trip.