The Blackjack Nature Trail itself is very short and not too spectacular (at least when we visited). The trail itself was wide enough and moderately kept up, but the hike itself was quite boring.
The one interesting part of the hike is how the different types of terain covered in such a short distance: grasslands to forest to desert-y (plenty of cactus).
Solitude is so high as we did not see another person, car, or other signs of human life on or around the trail. The trail itself is located out of the way by a "group pavilion" and over-flow camping area.
We were not sure where to park, so we parked on the pavement (as required by signage), closest to the trees by the bathroom. All marked parking spaces seem to be for camping only.
"This book will be in great demand by travelers, park visitors, and aficionados of Texas landscapes."