It was discussed that horror films allow us to see vicious act while remaining completely safe. This is also true in videogames, but a degree of separation is removed. The character is not merely watched but to an extent the player becomes the character. One can control the actions; thus removing the, "Holy shit get the hell out of there!" shouts that plagues us when watching a movie. A good horror game makes the player realize some terror that the characters feel in movies. You cannot know the terror of running out of bullets until your faced with a horde of necromorphs or splicers (kudos to you if you understand my nerdtastic references).
Both horror movies and games are adequate ways of fulfilling our desires of terror; however, games would not be what they are without movies. Trapped in outer space on a ship with hundreds of alien being that were brought on board for the purpose of an organizations gain. Sound familiar? This is both the plot of the Alien franchise and the (AWESOME) game Dead Space. The first Resident Evil took place in an abandoned mansion with terrifying zombies, giant spiders, and a giant snake. The original version of the game released for the Playstation feature live action segues that featured featured some of the most horrendous acting on the same levels of b-movies.
I'll end this post by saying if you want a good scare with a plot that's honestly better than most horror films being spewed out today go find yourself a nice and scary game. Bioshock and Dead Space are two beautifully written series with great scares.