Less than ideal casting to my mind. They decided to ride a bandwagon of known actor, with a huge burgeoning following, and it was purely Cumberbatch's acting coupled with some avoidance of certain characteristics that made it serviceable. Focus on his quest for vengeance - in this case against Admiral Marcus and not Kirk - and replace the fierce passion Ricardo had under control, with a cold and creepy aloofness brought by Benedict. It could equally have been Benicio Del Toro and worked in a vein closer to the original.
Personally I would've been super politically correct, and I don't know, cast an actor of actual middle-eastern decent, or an unknown Bollywood actor, or anybody capable of more convincingly being connected with the character's background established. Ben Kingsley maybe? Anybody but Cumberbatch. You start with what is established onscreen in the two previous encounters. The surname is Singh. He speaks of having been a Prince. An historian paints a picture of him in a Turban, which the character sees and approves of. Then there's the costume design from "Space Seed". I'm thinking of the gold suit Ricardo wears to dinner, which resembles something from an Indian wedding. There's the headgear he fashions to wear to protect him from the wild winds of Ceti Alpha V.
I enjoyed Into Darkness despite myself, but those underlying issues bother me deeply. I can't seem to get past the fact this casting wasn't as carefully considered as any of the original crew, which involved their approval or their relatives in the case of deceased. Which brings me back to De Toro whose name was in the frame early on, and has subsequently proven he clearly didn't mind dabbling with sci-fi if Guardians of the Galaxy and upcoming Star Wars VIII are anything to go by. His agent asked for too much money I assume, and got realistic in time for Guardians.
Anyway, I don't see how this plot works with anybody else but Khan Noonien Singh.
Had it been Gary Mitchell, what's his motivation in regards to the torpedoes or assisting Admiral Marcus for instance?