In all honesty the two depictions of the characters couldn't be further apart. They might as well be two different characters the changes are that extensive.
But they really aren't. Both will manipulate you and pretend to be your friend as long as it suits them, then turn around and stab you in the eye with a fork.
Both were quick studies, becoming familiar enough in a short time with the Enterprise and its operations to effectively destroy the ship...
...and both were willing to do so, because in all three of his appearances one of Khan's defining characteristics was that when his will was thwarted by an enemy he was willing to destroy both them and himself in order to avenge the loss.
I thought Cumberbatch was an excellent Khan and in keeping with the character we saw in TOS.
For those that Cumberbatch's appearance really bothers, they can go read Star Trek: Khan from IDW. It spackles over the discontinuity.