Moss, your picture here is a help in imagining what it will be like
http://www.themodernantiquarian.com/post/50388
when compared with this map -
http://www.savestonehenge.org.uk/shplan.gif

I'm not sure how far along the cutting you would have been standing (do you?) but it will run in for a third of a mile getting deeper and wider and culminating in a big black tunnel entrance with lights in it directly facing you. Nice. Same thing at the other end but longer.

As someone mentioned elsewhere, won't it look nice at dusk when the whole thing's lit up?