The kingdoms of southeast Asia (Cambodia, Indonesia, Thailand and Vietnam) are called "lost kingdoms" because, "identities and sometimes very existence only emerged from the historical shadows in the twentieth century, as a result of pioneering epigraphic and archaeological research, much of it recent."
Writing about the exhibit in the New York Times Holland Cotter noted that the beauty of the exhibit will carry you through. He noted that "everywhere here, in choirs of Buddhas with self-possessed smiles and hands like flowers, in Hindu gods with stern adult faces and the lithe, barely dressed bodies of teenagers at a beach."
The Times has a nice slideshow of some of the image and you can also view many of them on the exhibit site. You can watch a short clip below about the exhibit form the Voice of America. And the Huffington Post has a series of great photos worth viewing.