We enjoyed everything about Grand Isle and only wish it hadn't rained. Every. Day!
Oh well, our grassy site (#80) was a fine refuge for three nights in a tent. It was level, free of roots and stones and far enough/close enough to the bathroom.
Bring quarters for the showers (and pay it forward).
Bring your bike - lots of safe, local (flat) roads both on and off the campsite. Make sure you explore all the islands. (There are two nearby breweries.)
There's a so-called beach on Lake Champlain, but you probably wouldn't spend much time there. I like that they have a Dog Beach.
There are lots of signs warning against late-night noise. But the only thing I heard was a couple coyotes (I think).