|Season 1 is basically an introduction to the "new" Sherlock Holmes, and sets the stage for his battle with his arch-nemesis, M . The arch-nemesis recurs through all three episodes, weaving a web through the various plots.|
Holmes himself is established as a "high-functioning sociopath" who is bored without an intellectual challenge to stimulate him. He's willing to put his life at risk to gain that stimulation.
Despite some initial difficulties with his leg, Watson seems to have settled in. He seems to be looking for a regular woman in his life. However, there don't seem to be any surprises, other than a willingness to kill to defend his friend.
The other element introduced is Mycroft Holmes, who appears to have his brother's best interests in heart... even if they disagree about what those best interests are. Mycroft remains a manipulative individual who is more than happy to use his government resources to track Sherlock and John.
Season 1 puts the pieces on the board: Season 2 will presumably be how the game proceeds. Assuming Sherlock and John survive the season finale, of course...