The show returns in the New Year and covers some of Arthur Conan Doyle's most famous novels in the series, with episodes 'A Scandal in Belgravia', 'The Hounds of Baskerville' and 'The Reichenbach Fall'.
"[Sherlock is] slowly gaining a humanity," Cumberbatch told The Guardian. "He's on the side of the angels. His methods are definitely devilish, but he's got good at the core."
Show co-creator Steven Moffat added: "On the journey that Holmes is on, he's sort of realising that he's not completely amoral. By meeting Moriarty he realises that he's not [evil]."
Andrew Scott will return in his role as Moriarty following a cameo in the finale of the first series.
"He has this amazing ability to conjure up this sort of blank-eyed desolation of a man too clever, too clever to exist almost," Moffat said of Scott's portrayal.
Sherlock also gains a love interest in the new series in the form of high-class dominatrix Irene Adler, played by True Blood actress Lara Pulver.
"Very beautiful, incredibly smart, quick thinking and resourceful," Cumberbatch said of Irene. "She's got a lot of attributes that mirror his. She doesn't suffer fools gladly. [Sherlock] has a blind spot which is female emotional intuition.
"He's very good at guessing the kind of everyday circumstances in the sexes, the normal nuances of courtship, but I think what she has is much more complicated than that."
'A Scandal in Belgravia', which picks up where last season's cliffhanger left off, airs on BBC One on New Year's Day at 8.10pm.