As other reviewers have pointed out, some of Freud's groundbreaking theories have since been challenged, moderated, even overturned - but that doesn't render this book irrelevant to current readers and students. What is so critical about Freud is that, like Marx, he fundamentally changed the way we think about 'man' and what it means to be human.
Freud's understanding of the unconscious and particularly his work on dreams and the work they do ('dream-work') effectively rendered a person mysterious to themselves, challenging, for example, Descartes' view that the human mind - and, therefore, man him/herself - was completely knowable.
Freud, thus, has a huge impact on the way in which we think about what it means to be human, and the way in which 'humanness' is represented in, for example, art and literature.
For a scientific text this is immensely readable, even playful and mischievous in parts. We may have moved on from a literal application of Freudian theories, but this is still a ground-breaking text in the history of human thought, and one which still has implications for the way in which we think about ourselves, the products of our imaginations, and the way in which we create meaning.