We visited in June 2021. Drove all day from San Diego through Three Rivers and up Mineral King. It was just as treacherous as we'd heard. The campground is lovely and I would definitely go back if it weren't for that road.
Sites were fairly distanced from each other, trees provided shade but it still got quite hot in the middle of the day. River was cool and safe to play in and provided a lovely white noise, but the mosquitos in the evening and the flies in the day were no joke.
Had to carry our gear into our walk in site (that was all that was available to us) which was a beautiful long walk (under 1/4 mile) and would have been totally tolerable if you think of it as backpacking instead of inconvenient car camping. We bear boxed diligently and marmot-proofed our car and had no problems, never saw either.
We walked 2.7 miles on the "road" back to the Silver City Resort for pie and cold drinks one afternoon. Walk was long and hot but snacks were on point.
Vault toilets were better than I expected and a longer walk from our site than expected.
Pack light. Prep for critters. Bring bug spray. Come when it is cooler than in July.