The Starfleet officer who exceeds his authority, and crosses the line had been done to death in almost every Trek series, and the disaster porn at the end did not sit well with me.
That Peter Weller had already played an evil character who thought what he was doing was “right” on Enterprise didn’t help.
They only used Khan for the name recognition. Cumberbatch could have been playing just any old genetically superior madman. I saw nothing of the Khan that Kirk and company had a grudging admiration for in Space Seed , much to Spock’s puzzlement.
Of course, I know someone who isn’t that familiar with classic Trek, and has never seen TWOK, who thinks Into Darkness is great. 😉