(or "Turn And Face The Strange Ch-Ch-Changes")
Looking at 'Killraven' as a concept, it shouldn't surprise any student of comics that the original concept came from Roy Thomas. The man is a loyal fan of classic pulp fiction and Golden Age comics, having championed Conan, the Justice Society, and (in his various stints on Doctor Strange) H.P. Lovecraft. So, "The Martians from 'War of the Worlds' come back after getting their shots," well...yeah, that's a Roy Thomas concept, alright.
That pulp influence shows throughout the storytelling engine. Killraven himself is a sword-wielding, brash, tough-talking former gladiator in the Martian slave pens, who's escaped with a battle-hardened band of his comrades and wanders the Martian-ruled former United States seeking for a way to overthrow the cruel tentacled tyrants. It's set a few decades in the future, so you can have flying cars and ray-guns to go with your swords and horses; the ruined USA is your setting, with each issue taking on a sort of travelogue motif; the dialogue and tone are all very much in the 'Conan' vein, with Killraven and his first lieutenant, M'Shulla, faux-bickering in the manner of Conan and his trusty ally of the month (I'll admit it, all of Conan's buddies blur together in my mind. The 'Essential Conan' is out of print, too, so I'll never be able to get them straightened out...)
This probably isn't going to win the Pulitzer Prize anytime soon, but Thomas has laid us down a template for fast-paced, pulpy fun. But he was also editor-in-chief at the time, and that's something that cuts into your writing duties...so he took the idea of Killraven, and after only a couple of issues (which also included Gerry Conway and Marv Wolfman taking a hand), it passed to Don McGregor.
McGregor, though, wasn't interested in telling the stories Thomas designed the engine to run. He was more interested in using the ruined USA as a vehicle for social commentary on present-day culture, and although the Martians remained the series main villain, they faded a bit into the background as the setting became more of a character in its own right. New characters were introduced like Carmilla Frost, who were a bit more introspective and suited to McGregor's style, and Killraven himself seemed a bit out of place in his own title. (Indeed, his constant arguments about Frost's "overthinking" seemed at times to be arguments with the writer as much as with his comrades-in-arms.)
Was the sudden shift in tone successful? It's difficult to say. Certainly, there's still a strong core of Killraven fans who think that McGregor's melancholy pieces are more interesting than Thomas's initial broad strokes, but I can't help but wonder what the series would have been like if Thomas had picked a writer whose vision was more consistent with his own. Because tone is one of those subtle things, but changing the tone of a series can be every bit as big of a change as killing off a supporting character. After all, if you're not interested in writing fast-paced pulp adventures of a brash, tough-talking gladiator, why did you sign on to write 'Killraven'?