I watched this episode, aged 11, in the UK in 1970, and it 'was' (then) disturbing to me; and it was still a powerful watch in 1992, when next shown again, and in later years when I watched it with my own kids (then) as youngsters; all the good qualities one associates with ToS Trek at its best were on display: story, script, direction, photography, acting, the guest stars, the production, the music, and the music editing. It's stood the test of time. UK lifelong Trekker.