I just don't ``get'' halter dresses, blouses or any other garment in this configuration. The few times I've worn anything like this, I've hated having my bare shoulders sticking out. And I honestly don't think it's an attractive line on anyone, much less the royals in their designer halter frocks. Your mileage may vary, but they don't do a thing for me.
I think it depends very much on the shape of the dress and the shape of the person.