As many have noted before, the Call of Cthulhu game is really more like "H.P. Lovecraft meets Robert E. Howard" than it is pure Lovecraft. A pure Lovecraft game would be pretty boring... characters investigate, then they run screaming or go insane. The end. That can make for a good horror story, but as a game it would be pretty pointless. I think the game, and most of its published scenarios really, do a pretty good job of balancing these two. Lovecraft's mythos and his cold, uncaring universe are preserved, but characters can fight back and make a positive difference, even if only temporarily.
Personally, I've never liked adding ghosts, vampires and werewolves to CoC games. I also personally don't like mashing up other genres, with it, but that's just me. But the fact that investigators might team up and go after cults or do what they can to combat the Mythos doesn't bother me too much, even if it's not what Lovecraft wrote. If the Mythos and its cults were real -- and that's what we're pretending when we play one of these games -- then not everybody who encounters it would be a high-strung, nervous, solitary academic or antiquarian like Lovecraft's protagonists. What if Lovecraft's protagonist was a tough P.I. ex-combat soldier? What if he was a reporter, used to hanging around gangsters? What if the protagonist was a woman (of any stripe, since HPL never used them as main characters)?
The only unbreakable rule for me in a "Lovecraftian" game is the preservation of his view that the universe doesn't care, humanity is insignificant, and the only gods that exist either do not care about us or consider us as pests to be cleared off the Earth.