This episode is burned in my mind for the "One Riker, one bridge" scene. I think they were still working on Worf's characteristics here.
That episodic promo sure looked exciting, I'd love to see that episode one day!
Still a very spooky feeling episode even if the conclusion is a bit contrived; I used lab mice to complete my Physiology degree and if one of them had threatened to blow themselves up rather than continue with the experiments, I would have been more inclined to carry on studying rather than release it. This episode has a nice "old-trek" vibe to it, ie, exploring the unknown. I had not realised this was a bottle-episode before this rewatch - definitely one of the better ones.
"Yes, absolutely, I do indeed concur, whole-heartedly"
"A simple 'yes' would have sufficed Number one."
I agree with you about the episode having a creepy or spooky vibe to it, and also that it has a very "TOS" feel to it. An interesting riff on the "subject of advanced alien experiments" that was a pretty common Trek plot idea.