Seconds was not a hit when it was first released in the fall of 1966, but I recall interest in the movie being kind of high in my household at the time, when I was seven. My parents were not what one would nowadays call cinephiles, but they did, as they used to say, like movies, and they kept up with them to a certain extent. My mom, like, I suppose, many women of her generation (she was a couple months shy of 28 at the time of the film's release), was an admirer of Rock Hudson. She also enjoyed, to an extent, horror movies (it was at her behest that I had seen my first horror picture, The Haunting, a little prior to 1966, on the television, on an evening when my dad was working and she didn't want to watch alone). Seconds, then, was a movie that intrigued my mom and a lot of friends her age because a) it was an unusual picture, a disturbing picture, but also a "modern" picture, a picture about what was happening "now;" and b) because its central conceit had an old person who hated his life undergoing a seemingly miraculous transformation into, well, Rock Hudson.
In a sense that conceit seemed almost a joke, and in the DVD supplements I've looked at on Criterion's excellent new edition of John Frankenheimer's picture, both Frankenheimer's widow Evans Frankenheimer and the movie's female lead Salome Jens discuss the pains taken to make the transformation as credible as possible, how when Hudson first appears in the film he's still got the white hair of John Randolph, and convincing plastic surgery scars and so on. He only becomes dreamboat Rock after the scars have healed and his character undergoes extensive physical therapy and training (acted out by the fit Hudson in baggy sweat shirt and pants).
But it seemed like a joke, or a potential joke, for different reasons that it might to the contemporary cinephile or quasi-cinephile who's swallowed a lot of the conventional wisdom on Hudson, as in the multiple commentors on Dana Stevens' solid Slate consideration of the film who want us to make sure they are aware that Hudson wasn't much of an actor. Considerations of Hudson's acting ability (which know-somethingish types will forever continue to underate anyway) were not paramount to whatever appeal Seconds might have had; no, what made the Rock Hudson idea potentially funny was that it was in a sense too good to be true. This Rock Hudson was Hudson before his forced outing. The phrase "the man every man wants to be, and every woman wants to be with" or whatever it is, had not been coined yet (I don't think), but that is in fact the ideal which he represented to middle-class American pop-culture consumers. But at the same time Hudson himself, and the whole idea of the matinee idol, period, were on the cusp of cultural obsolescence. There's something about this fact, and the fact that Seconds was shot in black-and-white, which was then at the time supposed to lend a "documentary" or "real-life" feel to film footage, that added to the particular power with which the movie resonated at the time with the people who saw it. People who were not, as it happened, particularly invested in seeing Rock Hudson redeem or prove himself as an actor.
Because the matinee idol did not have to be an "actor;" performing virtuosity simply was not where their value was located. As it happens I believe Rock Hudson a very effective performer who may well have been a good, or "good," actor, and I think that it's almost neurotic to preface any assessment of his work with an assurance that you "know" he wasn't all that talented. With the exception of, you know, something now rightly deemed impossible in hindsight like Tazu, Son Of Cochise, Hudson was more often than not entirely right in executing the particulars of each of his film roles. Above and beyond the amusing MacMahonist notion (applied to Charlton Heston, as we recall) of physical beauty so acute as to constitute tragedy.
But it is still to Hudson's credit that when seen today his work in Seconds can live up to expectations that his actual audience didn't even think to entertain in 1966. His performance is remarkably somber and yet he doesn't make it drag on the audience; he seems to instinctively understand that a brooding Rock Hudson is still pretty easy on the eyes, which frees him up to really brood—not go "ultry-sultry" but look as if he's just been informed of the actual existence of death or something. Some sources say that he made the movie at around the time he was just beginning to share the reality of his life as a gay man with some of his friends; arguably, this dimension added some genuine depth to the who-am-I tortures his character puts himself through.
It is worth remembering, too, that sometimes Hudson's closest collaborators and biggest boosters could underestimate him. In the volume Sirk on Sirk the great director, who steered Hudson through several wonderful films, recalls choreographing Hudson for 1957's The Tarnished Angels: "There are some lines [from 'The Love Song of J. Alfred Prufrock'...] I read [...] to Hudson in order to give him an idea of what Faulkner had in mind for the reporter character"—the lines are those beginning "No! I am not Prince Hamlet," and ending at "at times, the Fool"—This is what I wanted Hudson to be, and I told him so: 'You are not the Prince in this movie,' I told him—'that's Stack.' To my surprise, he understood, although he knew that this meant in a way he would have to play second fiddle."