Abject pandemonium to get into the memorial, and then terrible disappointment. Long lines to get the tickets, for which there is no charge (if you reserve them online, you can avoid the line for a $2/ticket administrative charge). Then you walk several blocks to get to the crowd (not even a line, yet) gathering outside the "entrance"... eventually, you move into line formation, right next to the people who do not have tickets! ...go through security, walk around the corner and down one block, to enter the courtyard, where there are two, very interesting pools where the North and South towers stood... VERY anti-climactic.
The building is not open to the public, yet, and when it does open, you will be charged.