Like most of the rest of mankind's efforts, paperback book cover art falls mostly in the "competent" category, with some examples being truly lousy. And of course there are some artists whose work stands out, transcending what many might consider "trashy" subject matter. So I think it was for Orbik. The guy had a solid, painterly style along with the ability to create interesting dramatic settings and artistic compositions. I need to add that his book cover illustrations had to include space for the title, author's name and other elements, so this context needs to be taken into consideration when evaluating composition.
His web site lists the following illustrators as inspiration: "Robert McGinnis, Gil Elvgren, Dean Cornwell, Mead Schaeffer, Andrew Loomis, John Buscema... and a healthy dose of Norman Rockwell." For some reason he didn't note his teacher Fred Fixler, whose commercial work included paperback book cover illustration.
Orbik's style is characterized by strong, well-placed brushwork based on a framework of solid drawing ability -- yes, he did use photo references, as do most illustrators. Take a look.