I enjoyed this for what it was: a failed television pilot from 1972. Taking into account the era in which it was filmed, it's quite fun. Despite being a supernatural thriller, there aren't much in the way of special effects to be distracted by: most of it is make-up / in-camera effects. The most glaring "wow, look how far we've come" moments are when Nimoy is being the wheel of a vehicle (his race car at the start, and a nicely-restored oldster later in the movie) and when anyone falls out of a window or off a cliff (which, between visions and actual events, happens at least 3 times that I counted). Otherwise, the mood is set by the set lighting, the actors, the wardrobe and the make-up. It's amateur-looking by modern standards, but I ignored that and just had a good time watching it.
Concept wise, I'm really surprised this concept hasn't been picked up for a remake in more recent years. Given the plethora of supernatural shows on television (mostly on the CW, but also on the major networks) as well as the number of "charming lead man investigates crimes" shows, I would think someone would have revived it.
Cast-wise: Nimoy is a charming and engaging leading man who despite the evidence around him is still not sure he's actually gained supernatural abilities until the very end of the episode. The visions are his only ability, so he still needs to think/fight his way out of tight spots the way anyone else would. Susan Hampshire is equally as engaging as Michele Brent, and there's a definite playful chemistry between the actors that makes the blooming romance between Kovack and Michele believable. The rest of the cast are listed as "guest stars" as they would be on a regular television episode. Vera Mills is perfect as Andrea Glenn, the US actress on British soil who is the intended victim of a convoluted scheme to kill her off and gain control of her daughter Jennifer (played with wonderfully eerie self-possession by Jewel Blanch). Rachel Roberts is great as hotel owner Mrs Farraday, just this side of over-the-top as she reverse-ages through the episode. And of course every British drama has to have a Grande Dame -- Valerie Taylor does a solid job as the mysterious Louise Sanford.
Plot-wise: Well, the show has a great concept but there are some unavoidable plot holes and otherwise cheesy moments. Italian houseguest Verelli's knowledge of the secret door to the wine cellar felt like it came out of nowhere, as did Michele's knowledge of the "special sign" Kovacks needed to use toward the end of the episode. During Kovack's "near-fatal" car crash at the start, the paramedic's attempts at CPR, while Kovack is still in the race car in a seated position, are laughably fake. And just who was driving the beat-up old van that follows Kovack and Michele on their little afternoon joy ride? The director assumes we'll figure it out. There are some continuity issues with what time of day things are happening. And there's a great Mission: Impossible-like moment near the end as well that's just ... well, I laughed because it felt so out of place.
I watched the 89 minute "UK Cut" of the pilot. The disc also includes a US cut that is 10 minutes longer, but I haven't had time to screen that. If/when I do, I might come back and add some thoughts to this post. Especially if some of those plot holes are filled in.