Most "Twilight Zone" episodes are trite garbage, and this one is no different. It's "obvious" to a fault -- you know exactly how it's going to end right from the start. I'm giving it a 10, though, simply because of Robert Duvall's exceptional performance.
It's of a quality one would expect in a feature film. His character is distant and unsympathetic, not the way one would expect the protagonist of such a story to be played. But it shows just how unable he is to get along in this world.
I've probably seen every episode of "The Twilight Zone", and I don't remember any performance remotely as good as this one. Indeed, it's one of the great performances in the history of series TV.
An addendum... I note that /my/ rating for this episode is only three "helpfuls" out of 31. (I see the same thing with my Amazon reviews.) It appears that readers are looking solely for confirmation of their opinions -- not any insight into the episode.
The fact is that "The Twilight Zone" /was/ a highly uneven series. Much of it is, indeed, trite garbage -- heavy-handed "message" stories, tales with trivially ironic or O Henry-ish twist endings. Is the fact that "Miniature" was written by Charles Beaumont supposed to add cachet to what is a shallow and worse-than-mediocre story?