Big update as of spring 2021: Hoh is now a reservation campground.
First of all, what a privilege it is to stay in such a unique and beautiful place like Hoh!
Campsites are either a huge hit or a huge miss. Because so many people are visiting and camping during COVID, we were unable to get a good spot the first night. The spot we had was virtually impossible. The tent pad was extremely lumpy and there was nowhere level to set up. Fire ring and table crowded in together. Rocks everywhere. No privacy from neighbors and we really felt like we were on display.
The good news is that because Hoh is so high traffic, people seem to come and go quickly. The next morning we were able to snag a river spot and it was easily one of the best sites! Huge site, lots of privacy. However, once again there were rocks everywhere! It was shockingly hard to drive in our tent stakes (and take them out!). We had to dig out rocks for about ten minutes before getting everything secure.
Being on the river was amazing. Though one downside is that it's such a cool little area, people were walking through the back of our site a lot. It was also a great place to view stars.
Another thing to be aware of is not only can it rain (in a rainforest!), it can get pretty cold at Hoh. Our first night was 46 degrees.