We stay at Cossar pretty often, due to it being close to home. We have always stayed on the Yocona Ridge loop, and it has been a nice campground. The facilities are dated, but they keep them very clean. We did drive through the other loop (it was empty and closed at the time, the ranger let us look at it) and it appears to be much older than Yocona Ridge. There were trees/limbs down everywhere and the sites were pretty close to each other.
We had decent cell phone service here. There is no park WIFI. There is a Frisbee golf course that has gotten better over time. The course is now marked very well. The miniature golf course is old, but kids will still like it.
Some of the campers are also employees of the park. One lady just kept coming over and talking non-stop on this visit.