This is a bit out of the way compared to other drive up campsites nearby, but we came on a Friday night in the middle of the summer, it was the sixth campground we checked that night, and the only one that was not full. About half of the ten or so campsites were occupied. The drive in is not entirely paved, but there weren't many potholes and our little car did just fine. It took about thirty minutes to get to from the 101.
Getting there, you can either take the south shore or north shore road of lake Quinault. The south side is more paved, and there are more farms you drive past. The north side seemed a bit more rugged, there was a small bridge you cross that was 'interesting', and there were good views of the forest and lake.
As opposed to other campgrounds I have stayed at in Washington, this campground is in the Olympic National Park, and so the rules and atmosphere are a bit different than in the state park or national forest. For example, dogs are not permitted here technically (we had a dog). Also the only bathroom facilities are port-a-potties, which badly needed cleaning. So don't come here for the deluxe European style camping experience.
What this campground does offer is that it is directly in the old growth rainforest that is otherwise quite difficult if not impossible to access. Your tent will sit among thousand year old trees. It also rained, despite it being August, but it was a warm, light, refreshing rain that did not get you wet.