Amazing location, you're almost in Canada
I spent a few nights here in October and it was absolutely stunning! Ross Lake is beautiful, clean and crisp. We happened to be here during a full moon and the amount of light throughout the night was absolutely incredible. The sites are spacious and several are along the lakeshore. As for spacing, they seem adequate but there weren't many other visitors when we were there.
We hiked along the PCT to get here (with a side jaunt up Desolation Peak). We camped at several backcountry sites along the way (we started at the East Bank Trailhead) so this was a welcome home to wrap up our journey. We were fortunate to take a boat ride back to the other end of the lake to end our trip.
The Canadian boarder can also be accessed on foot from this park. The trail signs are measured in kilometers as well as miles, always fun to do the math.
There is running water here but I'm not sure about electric hookups (we didn't have any at our site). Sites do have campfire rings and durable bear boxes. We did experience a large rodent presence so be sure to keep your food and any salty (from food or sweat) secured otherwise they will find their way into it.