Spent 5 nights at Slerpy Hollow recently. All of the staff were very friendly, the grounds were tidy and well maintained. The bath house and laundry facilities were always found very clean, even in the evenings.
This location for our trip was perfect with an enterance to Badlands National Park just minutes south of town and access to freeway ramps either direction exiting the campground. Historic Wall Drug is just a short stroll away. Rapid City is about an hour away for any and all "big city" needs as well as access to everything else the Black Hills has to offer. We even made the 2.5 hour drive to Devils Tower.
The only things I could see as cons are:
There are train tracks that run along the East side of the property and are active late night (10 pm-Midnight roughly, I never actually looked to see if it was consistent or random) for a few minutes and then are gone.
Sites are a bit on the tight side but noise from other campers was never an issue for us. We just travel with our kids and they can get a bit spread out and wander from time to time so having a little more space to designate as "theirs" is nice, but we got by.
Having the playground on-site was also very nice. I also saw there was access to the Wall public pool a few blocks away that has a larger playground if needed. We usually camp at State Parks in Minnesota which don't always have playgrounds. Having somewhere to send the kids within eyeshot while getting food ready or things cleaned around the camper is always appreciated.
None of these "cons" would prevent us from looking at staying here again. We thoroughly enjoyed our time at Sleepy Hollow. Thanks again!!