Crowded in the summer, party island!
This spot (appropriately 5 miles from the Hoh River trailhead) is a great choice for a day hike or an overnight spot if you have enough time to make it this far into the backcountry before nighfall (if not try Mt. Tom Creek). With that being said this place gets really crowded with overnight campers during the summer so if your idea of solitude is hearing elk bugling in the morning you're better off pushing on. If you have a big group and don't mind seeing your neighbors this spot may be a good bet for you!
Located directly on the river with at least one privy (which probably gets utilized a lot) and directly off the trailhead this campground is just past the point that most day hikers turn around, so you won't have too much trail noise. There's a number of spots both on the side of the river and more than likely across the river on the island itself (although don't cross unless you know what you're doing). All the spots I noticed had fire rings and some had make-shift seats. Like all the spots long the Hoh River Trail there are bear wires here so no bear cans necessary although when I was there reports had come in of a curoius coyote who was stealing food/bags/clothes from the camping area!
Overall you're still going to get an outdoor experience here at 5-mile island, it's just how much solitude you want that will dictate if this is the right campground for you. In my opinion, if you have time pushing for Olympus Guard Station is a better option or stopping at Mt. Tom Creek.