The Zero Effect and the Downey movies also opt for Adler being both a criminal and in love (psychopath style of course,) with Holmes. And maybe the BBC version too, but I can't remember that stuff too well. So I can't agree that this is such a novel twist. Having Adler be neither, as in canon, would have been more original by now.
And bending the plot around to keep the population of the series' world small doesn't really seem such a good idea. Presumably Sebastian Moran was sent to New York to give Holmes closure when he caught and killed "Irene's" murderer? Or was Moriarty smart enough to predict that Moran would talk and put Holmes on Moriarty's track? But, how does that set up the whole reapparence of "Irene?"
But Watson's key role in capturing Moriarty was genuinely novel and well done, to strong effect I thought.