I prefer primitive or dispersed camping because I usually like as much privacy as I can get when I'm camping, but with current fire restrictions I was limited to developed campsites if I wanted a campfire (and what's the point of camping without a campfire?). I was also planning the trip on short notice, so developed, reserveable campsites were in short supply. Then I found Reyes Creek.
The campground is very isolated. It's about a 40 minute drive from the nearest town (and therefore the nearest gas station or market - plan ahead). There is no power, or water. There's no cell service in the camp, but a 5 minute drive up the mountain there's a dirt lot they call the 'phone booth' that gets decent reception. The camp hosts were super friendly and helpful. There are 2 loops for campsites - the center of the main loop seemed pretty flat, but all the sites were visible to your neighbors. Sites on the outside of the main loop offered more privacy, but most appeared to not be very level, and not necessarily well laid out. I stayed in site 11 on the outside of the loop which was large and fairly quiet, but my 6 person tent just barely fit in between some trees which offered some shade and was only on a slight angle. The one downside was the bathrooms - vault toilets that varied in condition, but none that I used were particularly good. If bathroom condition is a major sticking point with you, you may want to look elsewhere.
As an added bonus, as isolated as the place is, right outside the entrance to the campground is a bar & grill called the Camp Scheideck Lodge. They have a full bar and great food (and the customer-only bathroom is a great step up from the campground). It just changed owners last month (second time in a couple years) and the new owner, Devin, is friendly and welcoming.
The temperature varies greatly from day to night (90's to 50's when I was there) and there are bugs a plenty, so bring repellant. Firewood is available at the camp, and ice is available at the lodge.
So if you want a little isolation with privacy, a campfire, and a friendly bar within walking distance, this place is for you. I'll definitely be coming back.