"I am a high functioning sociopath," Sherlock announces proudly. Although the Original character penned by Sir Arthur Conan Doyle was not really sociopathic, he was undeniably unique and separated from normal people by his abilities. This Sherlock, however, seems quite happy with his life, cut off from normal human emotional problems.
Funnily enough, this is something that gradually changes through the first, second and third series (seasons). He becomes more human, due largely to his growing friendship with John Watson, and to the mothering influence of Mrs Hudson. Many of the original character's deductions involved an empathetic understanding of human emotions, so how does our high functioning sociopath compensate for this gap in his personality?
Quite simply, by using his Mind Palace. Sherlock's mind contains a gigantic vault of information on almost everything. In that vault are many observations of human behavior made by experts in the field of psychology. Dispassionately, he can understand human emotions in a textbook fashion, a sort of: slot B joins onto tab C kind of way. Whether he really is a sociopath or has just built a protective wall around himself is open to debate.
Essentially, though, he is basically the original Sherlock Holmes, the same one-man band detective. Although he does occasionally get help from Molly the pathologist and from the police forensic department. Additionally, he has powerful tools that the original character could never have dreamed of - a smartphone and a computer.
The creators and writers, Mark Gatiss and Steven Moffat, are quick to acknowledge the original genius of Conan Doyle in producing such an amazing character.