I give this episode a rating of fair because, although the story had a strong as well as an interesting plot idea, the execution of this idea was lacking. I sat through most of the episode somewhat confused as to what was happening. I was also annoyed by the severe overacting involved (especially by the actress whom played the role of Gem), although I do acknowledge that this was somewhat necessary considering the fact that she was indeed, mute. Since this episode paid special attention to the theme of emotion and empathy, I as a Trek fan (as well as a Spock fangirl) expected a more memorable and involved part from everyone's favorite Vulcan, but I was indeed disappionted.
I believe that if the story line had permitted Spock to become the test subject, rather than McCoy, the episode could've been improved by at least 3 points. As I believe the psycological aspect coupled with the emotional one would've been more successful than, "Oh no, let's watch dramatically in our little rainbow tube in the corner as our friend dies slowly and painfully".