Manzanita Lake campground is one of those nationap park campgrounds with several loops and site after site. It is definitely not the most private experience, but one would know that going into it. As far as national park campground go, Manzanita Lake offers a great experience without feeling super crowded- national parks can become zoo-like (because of their fantastic preservation and good marketing :) ), but this campground feels more low key. I am more of a backcountry camper, and I would recommend this campground to a friend.
It is clean, relatively quiet, and has great facilities. It also provides good access to the rest of the park, being at the north end of beautiful rt 89 and just below the Chaos Crags. Everyone should visit Lassen and if you are looking for a campground, put Manzanita on your list.