There have been many movies and games more or less inspired in Lovecraft's writings ("The Thing" is the first one that comes to my mind) but the very essence of Lovecraftian horror makes it not good for movie or game adaption. This doesn't mean the movies aren't good by themselves, many are, but they simply can't convey the spirit of cosmic horror, which is not about the monsters or alien races he described but rather about our insignificance and vastness of the cosmos and all the horrors that possibly lurk there and possibly have lived and live here with us. Lovecraft's horror is about what is not seen, about the despair of little by little realizing one's insignificance in the cosmos and about there being many horrors that could drive you mad if you ever were to see them if you weren't blissfully ignorant and incapable to see.
I know the above did sound a little pedantic but the point is is that the main theme in Lovecraft is not "tentacles, aliens and fishmen lol" but the horror of learning about things that man was not meant to know, of indescribable abominations beyond the understanding of the human mind that you will lose all sanity and possibly die upon mere gazing, of the ephemerality of everything we hold dear including the very human race which is always at the verge of extinction were some unseen forces that we can't comprehend ever going to bother with us (ie: "the moment Cthulhu wakes up we're gone"). The tentacles and stuff is just the little the mind person can make up from seeing those horrors before going mad from contemplating them.
In short, Lovecraft's horror can't be adapted properly in videogames and movies because they are a more visual medium, and his horror is about that which is not seen and we can't understand. That's why text is the ideal medium for his works.http://tvtropes.org/pmwiki/pmwiki.php/Main/EldritchAbomination