We stayed at 3 different campsites as we took the entire Four Pass loop over four days. It was an AMAZING experience. All the campsites had amazing views, and most were incredibly private. The last campsite had the most people, which was the one by Snowmass Lake. Even though there were lots of campers and people at this site, it was still incredibly clean, and it was nice to gather and catchup with different individuals about our travels. Each of the campsites were clean and well maintained with a stream nearby for water. The trails were well maintained as well, but be ready to work hard as it can get a bit grueling and stressful. I cannot recommend this trail and its primitive campsites more. If you're looking to backpack with some amazing views, this is definitely the place to do it.
Also, thankfully no bears were encountered on our journey, but we did see a fox, a moose from a distance, and a deer.