This one is a 9 for me.
There are two scenes that I regard as masterpieces: listening to the Valiant
logs and the briefing room scene, especially once it's down to just Kirk and Spock.
The climactic fistfight being somewhat unbelievable to me is the only major minus, although I also think that the story sorta drags in the middle, in some of the sickbay scenes.
I could criticize the glowing eyes and the ESP angle as pulpy nonsense, but the attitudes projected by the characters, of being in danger and of utter seriousness, those more than compensate, I think.
With the series crew taking shape and the format getting ironed out, this
demonstrated the potential of the Star Trek
that was to come.