As you might have figured out by now, if you’ve been paying attention, I’m quite the fan of H.P. Lovecraft. Having written many short stories, few short novels and no full-length novels, it’s quite astounding that he has maintained such a following over all the years since his passing.
Part of that is due to the the dilligence of his friends with whom he shared a lengthy correspondence and their sharing of ideas and concepts. Even long after his death Lovecraft has continued to inspire and terrify.
And not necessarily in that order. 
Noted authors who have added to the greater Lovecraft Mythos (a term which I tend to prefer to Cthulhu Mythos) include Clark Ashton Smith, Ramsay Campbell, Brian Lumley and even, in his own way, Neil Gaiman. Stephen King has named Lovecraft as an early influence, although you’d never notice.
Generally I’ve enjoyed all the Mythos-related work I’ve found… except for one.
At the Mountains Of Madness.
One of Lovecraft’s first (IIRC) short novels which I’ve tried to read several times. This was in my teenage years and maybe it might have been too much for me to manage.
Now, as I’m rapidly approaching my 4th decade on this planet, I want to give it a fair chance now. I’ve been swimming in the Mythos pool for a while now and perhaps, just perhaps, that’s what it’s going to take for me to finally finish this.
We’ll see.
BigAl