And I do prefer Montalban to Cumberbatch in the role but that is 100% on the writers not the acting. Give Cumberbatch more development, more to do! Hopefully we get that next time around.
I think that Khan's speech in his cell describing how Marcus used threats to his "family" to control him was stronger, more human dramatic material to work with than all the "beloved wife" and Melville-quoting "from Hell's heart I stab at thee!" that Montalban was given to chew on.