My thoughts on the series
The TV series Kolchak: The Night Stalker ran for one season in 1974-1975, consisting of 20 episodes. Two additional episodes were scheduled to be filmed, but star Darren McGavin was becoming disillusioned due to an exhausting schedule and the fact that he was rewriting scripts plus doing much of the production work without compensation. The ratings were mediocre so he asked to be released from his contract with two episodes yet to be shot. The network granted his request in light of the ratings. I wish Darren would've persevered and finished out the season because then we'd have two more episodes to enjoy. He was too fatigued at the time to see that this unique and groundbreaking series would be his most well-known role, along with "A Christmas Story" (1983).
If you haven't seen the original two movies, "The Night Stalker" (1972) and "The Night Strangler" (1973), I encourage you to view them before checking out the series. The debut movie was the best of the batch with "The Night Strangler" almost as good and even better in some ways (see my reviews on IMDb for details). Both movies established the template for the series and myriad books that followed.
The 20 episodes are more of the same, but condensed into 51 minutes and all-around inferior. They're all of about the same quality with favorites emerging depending on how interesting the Monster-of-the-Week is, as well as the guest stars, both of which are a matter of taste. The first episode, "The Ripper," is a quality beginning for the series but it's too much like the two pilot movies for its own good, particularly the first film. It's basically a compressed version with a slightly different 'monster.'
"Horror in the Heights" is usually cited as the best segment because of the intriguing monster, which can mimic a person its victim trusts. It's actually pretty chilling for mid-70's television. "The Trevi Collection" is one of my personal favorites because it deviates from formula and contains a twist. The story tackles witchcraft but doesn't make the mistake of doing it in a one-dimensional manner (e.g. the mannequins). "The Energy Eater" is another fave due to guest stars William Smith, who beams with charisma, and professional-but-sultry Elaine Giftos, both of whom sorta team-up with Kolchak, particularly the former.
"The Vampire" is distinguished for its ties to the pilot movie and taking place in Los Angeles rather than Chicago, not to mention its vicious no-talking (and sharp) antagonist. "Demon in Lace" is one of the better episodes due to the intriguing succubus and the campus locale. "The Zombie" is notable for its formidable foe and one of the creepiest sequences in the last act at a junkyard. The monster make-up in "The Werewolf" is lame, but I favor the episode because it takes place completely on a cruise ship and features voluptuous & perky Jackie Russell as Wendy (in a black bikini), as well as Nita Talbot as Paula, who becomes Kolchak's gal pal.
The low points, for me, are the clunky "The Knightly Murders" (no pun intended), and "The Chopper," which devolves into camp. Yet even those episodes have their points of charm. The final segment, "The Sentry," is often reviled due to the reptilian creature costume, but it would've worked if the creators kept its cartoonish face & teeth obscured. The story rips-off Star Trek's "Devil in the Dark," but isn't anywhere near as absorbing. Yet this is partially made up for by the beaming & lovely Kathie Browne as Lt. Irene Lamont. Kathie was McGavin's wife for 34 years until her death in 2003. You might recall her as hottie Deela in Star Trek's "Wink of an Eye" from seven years earlier. Unsurprisingly, she & Darren have great chemistry.
The concept of the show, and its star (and some of the co/guest stars), are better than the actual execution of most of the episodes. The show needed someone of the caliber of Gene Roddenberry at the helm. As it turned out, the bulk of the pressure & work fell on McGavin's shoulders and thus he couldn't even finish out the season. Nevertheless, the show was seminal and acquired a cult-following, influencing more popular future series like The X-Files, Buffy the Vampire Slayer, Supernatural and The Walking Dead.