In of piece of Daniel's diary there is a nearly direct quote from HPL... something like "...impossible geometry and endless deserts...". Lovecraft used terms like these in many of his stories, especially in "At the Mountains of Madness".
Also the whole atmosphäre is "lovecraftian"
(and penumbra too)
Always alone, exploring deserted, ancient environments, supernatural events combined with science.
The monsters are very close to the monsters from Lovecraft, or at least they tried to get as close as possible. Of course they didn't include something like the Great Old Ones or other gods... I can hardly think of a way to SHOW them in any media...
But the implementation (not the visuals) of the monsters we know (grunt, brutes, shadow) is highly similar to the ones in Lovecraft's stories. You can hardly get a close look at them (if you are acting ingame like you would act in RL), if you try to, it hurts (mentally) and they have a very supernatural touch, escpecially the shadow.