Franchise Killer: The original series was abruptly cancelled mid-way through the second season due to poor ratings, although it would gain another life in syndicated reruns, and get a long running revival series decades later.
What Could Have Been: The 1998 version of The Outer Limits Companion includes an appendix which provides detailed plot synopses of TOS scripts and premises that were never filmed. It also has details on rewritten and Deleted Scenes from the finished episodes.
Vindicated by Cable: The first season was quite popular in it's day, but season 2's hit or miss quality caused it to take a nosedive and be cancelled. Fortunately, the show managed to gain a decades long life and recognition in syndicated reruns.