Onion Valley is way up into the Sierras, which means the views are amazing and it serves as a great jumping off point for backpacking trips.  Even if you are just going to day hike, it provides access to incredible country.  The sites are pretty private (sort of walled in by bushes, trees and rocks, with well-maintained fire pits, tables and bear lockers.  Just double check that your site is actually a drive-in site if that is what you want.  A few sites along the little road that runs through camp look like drive-in's but are not.