If anything identifies Freud as an innovative thinker it is his claim that there is an 'unconscious' mind which importantly can be observed and understood using scientific methods - of which, more later. Many other thinkers such as William James had already used the term but had made only passing reference to it - in discussions of sleepwalking, hypnotic suggestion and so on - as though it were one of those inscrutable facts of nature, which, whilst an interesting and fundamental component of the human psyche would remain forever shrouded in mystery.
Freud changed all this by elevating the concept into the realm of scientific enquiry by proposing the technique of free association as a means to uncover the unconscious thoughts which lay behind certain recurring preoccupations of 'neurotic' patients; however, it's validity was quickly demonstrated to be of universal application. The empirical data gathered by Freud consisted of the myriad analyses of patients which when combined, collated and viewed at length suggested to him certain universal features of this unconscious; the Oedipus Complex, the family of psychoneuroses and so on. In the main, the disputes among various schools of pscychoanalysis (Kleinian, Jungian, Lacanian, Adlerian etc.) centre around the manner in which the case material (ie. the evidence derived from the patient's speech) from analysis should be interpreted. Jung, for example, saw in the same material the evidence for archetypal components of the psyche and deplored the reductivity which seemed to crystallise the Oedipal relations.
It should also be noted that many analytical schools have refined and developed Freud's insights, particularly the Oedipus conflict. Deleuze and Gauttari's famous assault on the 'daddy-mommy-me' triangle (Anti-Oedipus: Capitalism and Schizophrenia) for instance, is scathing in its rebuttal of this fundamental postulate of classical Freudianism yet neither author would for a second refute the reality of the unconscious or their indebtedness to Freud's research. So, what all these divergent schools agreed upon was that there was such a thing as the unconscious mind; a domain which is largely inaccesible to us and which plays a significant, if not a dominating role, in determining our conscious behaviour. Again, the emphasis on just how determining this unconscious is and what implications should be drawn from this fundamental insight differ widely from one school to the next; the debate has never been properly resolved within psychoanalysis, nor is it likely to be.
Lacan once entitled one of his lectures; 'The Freudian unconscious and ours" indicating the necessity for psychoanalysis to re-establish its scientific credentials by examining some of the peculiarities within Freud's own psyche which led him to ascribe certain 'universal' properties to unconscious functioning. So, there was always a debate within psychoanalysis as to the ultimate truth status of Freud's observations since the findings which he had interpreted were being done (inevitably) through the prism of his own unique subjectivity. However, whilst this debate occurred, it is fair to say that the majority viewpoint, particularly within the British school, where the Kleinians were even pushing for recognition of pre-oedipal unconscious phantasies, there emerged a general consensus on the validity of a universal oedipal 'entanglement'.
In France, Lacan vociferously opposed this malaise and dogmatism. This necessitated a breach of sorts within the French psychoanalytic tradition and 'Lacanianism' is now synonymous with the attempt to fuse Roman Jakobson's linguistic researches into what he regarded as the structuring poles of language - metaphor and metonymy - as exemplary instances of the dream mechanisms identified by Freud, that of condensation and displacement. In the process, Lacan, quite correctly in my view, 'sublated' traditional Freudian Oedipal triangulation thereby giving the central concept of the phallus a more mobile and fluid range of interpretation - not everything was now reducible to this alleged universal dynamic or to the supposed formative crucible of the 'primal scene' (a postulated original 'traumatic' structuring event whose uncovering was held crucial to therapeutic progress).
Back to Freud - the 'royal road' to uncovering what meanings lay behind our conscious thoughts and actions is the dream since this was the unalloyed manifestation of the unconscious in action free from the interfering sensations and impressions of waking life. Freud studied thousands of dreams (of his patients and of himself) and determined that there were discernible mechanisms in action in the unconscious which could be understood and studied scientifically; namely condensation and displacement. It was in fact through empirical investigations which led to the discovery of these mechanisms in the first place. Now, this to me is the root of the Freudian discovery - if condensation and displacement do not take place in every dream then indeed the project of psychoanalysis may be labelled a fraud - but this is not the case, they are both empirically demonstrable and are in fact deceptively simple concepts to understand irrespective of what convenient straw man version of psychoanalysis critics such as Karl Popper have reputedly demolished through the falsification criteria - itself handsomely critiqued by Thomas Kuhn in "The Structure of Scientific Revolutions"