Burt Lancaster referred to this film as "'Death of a Salesman' in swimming trunks," and that's not a bad characterization. You could also think of it, in many ways, as "'American Beauty' in the late 1960s."
This movie came out nine years after the original 'Twilight Zone' series aired, and it would have made an interesting episode. As a movie, it lasts a little too long, is fairly melodramatic, and has some weirdly filmed scenes. Were they going for psychedelia? One scene in particular, where Lancaster simply crosses a busy highway, is just crazy with canted camera angles and weird zoom and blur shots. But one could argue that it helps build the dreamlike quality (or nightmare quality) upon which this story depends.
I am beginning to suspect that Burt Lancaster created the acting style most often attributed to William Shatner. That is to say, he's vain and overblown, he dramatically stares off into space a lot, and his disregard for personal space with women quickly becomes a little creepy. No means no, Burt Lancaster!
Maybe a lot of male actors were like this in the 1960s, I don't know, but it's a little odd from a 2016 perspective.
As weird and as dated as this movie is, it's a fun enough watch for a sleepy summer's afternoon — if only to see Joan Rivers' first dramatic role, and a brief scene with a young Diana Muldaur (Doctor Pulaski on 'Star Trek: The Next Generation').