TL;DR - Fine as a backup but the park is really more of a recreation area so definitely try to get one of the screened shelter or car camping sites (all of which have fire rings, picnic tables, and grills). 

We'd hoped to stay at one of the regular car camping sites in the park, but unfortunately they were all taken by the time we got to the site in the morning.

The park has ample day use facilities that you can drive up to, and the camp store is extremely well stocked. We swam, hiked, and kayaked through the park during the day, then two people in the group decided to drive back to Dallas that night while myself and one other hiked in to the primitive sites.

The hike in is about 2 miles. We took the designated "primitive campsites" trail hiking in. The trails were well marked, but pretty overgrown at parts with a TON of spider webs. The next morning we took the Cross Timbers trail back, which despite being a little longer was faster because of how much better maintained it was. 

We were getting to our campsite right as the sun was setting, so didn't explore much. Generally seemed like the different primitive sites weren't delineated very well, and as far as I know there's no map of the area to help. We managed to find a little outcropping that has obviously been used for a tent before. 

Would definitely visit the park again, and if needed camp in the primitive sites but take the Cross Timbers trail both ways.