I agree, Washington does seem to at least aspire to better roundabouts than some places I've heard of. The one rule I see to be truly necessary is "yield to oncoming traffic from the left."

I still get confused at the big roundabout in Kent, after coming off Highway 167 at Willis Street, but most others I've encountered are fine, despite the drivers who still want to stop before proceeding onto them even when there's no other traffic.