"adult" novelization (although the indicia states that it's based on Cover's book!) and is fairly faithful to the final film.
I didn't own a copy of this back in 1980 because I was a little old for it at the time, but I found a copy a few years ago. Great cover, eh?
Rumor has it that Williamson - who was both a big Buster Crabbe fan and had drawn several highly-regarded issues of Flash Gordon for King Comics in the 60s - absolutely hated drawing Sam Jones as Flash, and instead drew the character rather generically; this dissatisfaction with the art was why he subsequently refused to autograph copies of the book for fans over the years. I was also told (by one of Williamson's assistants) that that's why the Flash figure on the cover is a photo, while all the rest of the characters are Williamson's drawings. The licensors were unhappy with his rendition of their star.
I love this comic and own several different editions of it - the hardcover pictured above (which my wonderful wife bought me as a Christmas present a few years ago), the three-issue Gold Key comic book version, and the B&W reprint (from Williamson's original art) that appeared in the Al Williamson's Flash Gordon collection, which included every Flash story and piece of art Williamson ever did.