I'd second the recommendation for Camping Neptune. We've been several times now. It is a busy little site, but not 'bustling' if that makes sense. There's a cycle path alongside the river, and you can walk down to the Grau (beach) to the south, or north into the town of Agde (passing some nice restaurants along the way, including the one which Rick Stein featured on his French odyssey). The Canal du Midi is near enough for a walk, and there's lot more interest in the area.
The pool on site is very pleasant - not huge, but no slides and quiet. There are two toilet blocks - the shower areas are great, but alongside them are some 'squatter' type toilets - but around the back of the block are some normal English style toilet - no seats though, and take your own toilet roll. There's a small bar/take-away with tables which does a limited range of food. Pitches are generally a good size with differing amounts of shade.
Access roads can be a little tight on the corners, but manageable.