An excellent scene...but...
"You will STAY!" I think this is WAY over the top for Spock...I'd have had him say it in a cold, eerily calm and threateningly forceful way...Have him lean forward, his jaw set and say in a very measured tone, "You WILL stay.", the subtext being what he already said out loud; that there is no leaving without his permission, which he has no intention of giving...
...but to bark it like that was a bit much and out of character, in my opinion....just as a director myself...
I understand that we've seen Bones snap at Spock like this before, and I'm guessing the idea here was to show Spock reaching the end of his rope...but I just don't buy it. It's in times like this that we need to count on Spock to hunker down and set his defenses on high so this sort of thing doesn't happen. We admire, even envy Spock for not losing his cool in the face of such situations..and to snap like this is just off the mark...unless this is a road that Spock is supposed to go down in this particular story.......?