I can see how reading Call of Cthulhu
would be a bit of a letdown after all you hear about it, especially on the Internet. It's certainly not Lovecraft's best work.
It also makes most Cthulhu jokes kind of annoying, because they're always off the mark, pretty much just swapping him with Satan. ("Why vote for the lesser evil," etc.) I appreciate the jokes more when they're specific to Cthulhu in regards to the mythos. But all of that's just nitpicking.
To be fair to Stephen King, anyone writing like Lovecraft today would be laughed out of an editor's office for being so overwrought and using almost no dialogue.
What King popularized was the idea of supernatural horror in a modern setting, putting it right in a normal person's point of view. We forget that today because everyone's doing it now, but that wasn't always the case.
I often have a similar discussion with friends who draw cartoons. There's a tendency to dismiss most of Charles Schulz's work, but these people don't realize just how much he contributed. Kids having adult-like conversations, pets having thoughts and imagination--these ideas weren't popular before Peanuts.
Anyway, I'm rambling, but you get the idea.