The funny thing is that Stonehenge isn't strictly speaking a henge. A henge is an earthwork with a ditch inside a banked earth wall. There might or might not be stones inside the the earthwork.
Having been brought up on pictures of Stonehenge, I felt a little twang of confused letdown the first time I visited Thornborough. This passes quickly though, and if you're vaguely near North Yorkshire it's well worth a visit. I've had the pleasure of camping at the base of it a few times with fire and mead which makes it all the more fun.
Additionally funny (and ironic) that the term "henge" comes from Stonehenge, even though Stonehenge is technically not a henge.