Which shape? the outer sarsen ring? It's a circle (close to a perfect one too), but many stone circles across Britain and Ireland are circular (or eggs and ellipses).Nothing unusual in that.
The inner ring of trilithons is more interesting. They are the biggest heaviest stones,rising up to 24 feet in the western end (the half of the ruined great Trilithon). Now they are in an open ended horseshoe shape which is unusual in the British isles...but common in Brittany,France where they also built huge stone monuments in the neolithic.
the bluestones are interesting too. not only are they from Wales and form another circle and horseshoe, many of them have a decidedly human form,almost head and shoulders. they look a bit like some contemporary picture menhirs I've seen (again Breton influenced) only without the necklaces and face features.
The great trilithon was definitely aligned on the winter solstice and the heelstone outside the circle on the summer....but other alignments are less certain.
there were 4 station stones (only 2 remaining) set in a rectangle on the edges of the henge which, if you draw a line between them meet and cross directly in the centre of the circle.Again, rectangles aren't very common in ancient British stone monuments but ARE common in Brittany (a pattern emerging?)
Asfor the recent 'healing' theory, I have my doubts. life was hard, of course people in burial mounds had injuries. That is true across Britain. And people travelled more than thought, not just to Stonehenge. in Yorkshire the same isotope testing that told us the Amesbury archer ('king of Stonehenge') camefrom the Alps, showed another immigrant of the same period who came from the Netherlands.