First, I should note that Jason, fellow Alliterate and all-around good person, weighs on the six generations with the various Cthulhoid computer games. He puts them in Gen Five, but I think they are Gen Four - though at this point it may be more of a fine-tuning of what I mean by each group.
Second, noted game designerKen Hite has be engaged in a "Tour de Lovecraft", analyzing all of HP's fiction with his quirky and all-seeing eye. It's worth checking out.
Me? I'm still playing with the theory. Robert E. Howard should be in Generation 1 with Smith and Lovecraft, I'm thinking, but I don't really know where to put Ramsey Campbell and his Goatswood stories. I'm thinking Generation 2, with Carter and Derlith, but I can be argued otherwise. And I'm thinking that Generation 3 really is more of 60s/70s thing as well.
What, are you missing the pithy comments on collectable quarters yet? Don't worry, I'll get back to them, eventually.
(hmmm... in digging up that last link, I came across the entrance on that trepanation dream I had. Another Cthulhoid moment)