Its a wonderful and magical place.
Unfortunately is was slightly wet and cool when we went, but did not stop us (as we were prepared) Its a vast site with a great incredible honecomb of caves and monuments.
Its worth going early to avoid the crowds, have good walking shoes and be prepared for changeable weather early in the season Dec-Apr. Its in the mountains.
The Jordanians are friendly people and are not as hard (in your face) as the Egyptians when it comes to selling.