Yes, it's a loss of control but the way it was presented here was like watching Bruce Banner Hulk out; we can't wait until he catches up with the bad guys and gives them what for.
I feel that the first movie handled his outburst far more effectively, displaying genuine consequence, remorse and embarrassment. Having done so again in this movie (as part of its climax no less), a Spock-out has now become a thing that we're to look forward to and expect which I think is mistake.
I'm mixed on it. This was a much slower burn. In the first movie, spock lost his planet and mother and pointed out that earth was the only home he had left. The first half of the second movie had Spock in denial of his feelings. That's why he was so resigned to die on the planet. That's the point of Uhura's dialogue en route to Kronos and their later reconciliation. The second half saw Spock's suppression reach it's limits after he saw Khan "kill" Kirk and "raise his arms" on Uhura. Key point, Khan walks with murderous intent towards Uhura... Spock rips a piece of metal off the transport and beats Khan nearly dead in response... causing even Uhura to tell him to calm down.
Now Star Trek 3 could be more openly Spock centric since we've now wrapped up Kirk earning the chair he was given. Mind you, Spock saved the alien planet and stopped Kirks drone strike before beating Khan in both intellect and physical strength (while restraining himself from murdering Khan and his people) so this movie did have quite a bit of Spock's actions if not thoughts.