With its look ahead at old age for Kirk and company, this high concept episode became more and more interesting as Star Trek refashioned itself into various forms and fans were able to see the actors (and the characters) age legitimately. But is it a good episode? Sort of.
Despite not appearing on screen, makeup man Freddy Phillips is the real star, pulling off a miracle and turning the concept into a believable progression that happens before our eyes. Shatner, Nimoy, and Kelley deserve credit as well, selling Phillips's work with subtle changes in their characters' mannerisms that become more pronounced as the episode moves along.
But rapid aging is just a gimmick. Knowing it needs to be built upon a story, writer David Harmon attempts two different plots with mixed results. First, he throws in a passenger on the Enterprise who just happens to be an endocrinologist and also happens to be a drop dead gorgeous blonde with a fetish for elderly men. (Where can I find one of those?) And surprise, surprise, she has a history with Kirk, though they broke up so she could chase someone older (who has since died). Now, with Kirk prematurely turning grey, you can almost see her drooling as she reassesses his value. (Kirk: "What are you offering me, Jan? Love or a going away present?") As bizarre as it is to see her working with McCoy on a cure while eyeing up Kirk, the really weird thing is how this story all fizzles out and comes to nothing. Second, Harmon taps into the more natural idea of old age interfering with Kirk's ability to run the ship, a more successful plot element that forms the heart of the drama in the second half. (It's sort of the equivalent of an elderly grandfather not realizing he's losing the ability to safely drive). As the story works itself into a dark mirror of "Court Martial", the righteous indignation from that episode is replaced with a sense of pity here. Once again, Kirk must defend himself; only this time, he's in the wrong, and he's the last one to know it. (Unfortunately, the scene itself forces us to listen to characters describe sequences we just watched and gets a little tedious as a result).
Throughout the whole episode, of course, the ending itself is a foregone conclusion. Yet Harmon deserves credit for bringing back a throwaway element from early in the script and turning it into a clever escape route for the finale. Are there better Star Trek episodes? Of course. But there are none more unique, and even casual Trekkers should see "Deadly Years" at least once.
Remastered: With the focus on the makeup, the original episode doesn't have any fancy effects until the end; and those are taken from "Balance of Terror". That keeps it pretty simple for CBS Digital, which just has to upgrade a planet (originally an orange tinted version of the "Catspaw" planet), the ship, and a short battle sequence at the end.