Interesting the stuff you get when you pull out a random Kirby book.
GIANT-SIZE CHILLERS #3 (August 1975) reprints "The Monster", a 7 page story from CHAMBER OF DARKNESS #4 (April 1970). The credits have it as written and pencilled by Jack Kirby and inked by John Verpoorten, but that's really only part of the story.
Part of the background is told in THE JACK KIRBY COLLECTOR #13 (reprinted in the third COLLECTED JKC, with a teaser here), in an article that promises more details would probably be in Mark Evanier's still-upcoming biography of Kirby. In a nutshell, Kirby submitted the original story, was quite proud of it, then someone at Marvel insisted on wholesale changes, which Kirby made, and then Kirby scripted it, and Marvel made yet more changes after that. From the pencil and margin notes photocopies in the article, it was a much better story before the changes. With editorial help like that from Marvel, it's not surprising that Kirby took the contract DC offered not too long after.
The actual published story is okay, but nothing special. I don't know if my opinion is weighed down by knowing the background, or by comparing it to the original (which has some much nicer action scenes that are omitted in the final version), but overall it just seems to drift a bit and then just sort of end with a pat moral.
The art is still mostly good, and Verpoorten was a pretty good inker for him (Verpoorten only inked a handful of Kirby covers in that era, he was do some full issues of CAPTAIN AMERICA and ETERNALS when Kirby returned to Marvel). A few of the panels shown in the page above are close to how they looked in the original, and I just love the old-world castle architecture that Kirby does so well so often in his work (stories with Dr. Doom and the Demon being notable examples).