The sites are ok, and you can't beat the location. The beach is great but a hike from some of the sites. The flush toilets and clean showers are nice, however, they are very far from the outer tents sites. It is a long hike in the middle of the night. That being said, the sites smell like urine because the guys don't like the long walk after a night of drinking.
Clean restrooms. Coin showers available. BBQ pits. Recommend brining own fire wood. (Will last longer than the wood sold here for $7 a bundle). Close to restaurants if you don't want to cook.
San Clemente State Beach is fantastic, but huge. You have all of the positives combined with all of the negatives of a huge and popular campground. Summer spots need to be reserved the full six months out. Tent camping on the south and west sides can usually be pretty good, but there are chances that your neighbors can be drunk yahoos. It all depends on who is near you when you are here. If you have great neighbors, it will be a fantastic week! Party-bros and huge families... maybe not so much. The RV spots are packed in very tight. I only have experience with the tent sites. Easy access to the beach, and a quick drive or middle-sized bike ride into town for dinner. If you want a quieter spot, consider San Mateo campground. It is a longer walk down to the beach (Trestles) due to it's isolation.