A lot of people have been complaining and trying to convince others that adding a co-op option to a game in the horror genre is a bad idea. With the announcement of Dead Space 3 having a multiplayer co-op campaign, the amount of complainers rose tremendously. Yet people need to realize that just because a horror game has co-op, it does not mean that the game is not going to be scary or good anymore.
Personally i think that having co-op in Dead Space 3 gives players the option to be able to play the game with friends and experience the game in a new light. Walking through the lonely and abandoned halls of the Ishimura in the original Dead Space is a setting which is unforgettable. Some attribute the likeness of the game with the feeling of loneliness that the player feels throughout, just being alone on an abandoned ship with just a handful of others whom you rarely even encounter. This feeling of helplessness and loneliness is one of the selling points of the Dead Space Franchise, and you can still feel this in Dead Space 3 by playing the game without anyone else. As the developers have previously stated, the game will be able to be played solo in campaign, so you can feel the same atmosphere as you previously had in the other Dead Space titles, or you can play in the new Co-op setting.
Back to the topic of Horror games losing its scare factor due to having a multiplayer feature. The game will almost certainly play out nearly the same in terms of scares whether you play the campaign in single player or co-op. The only difference that we have seen when playing the demo is that the game has a more social feature, communicating with your partner while exploring this beautifully crafted atmosphere that Visceral Games created. The scares were still there, and one could argue that having someone else there diminishes this, and in a way it can cause this to some people. The slight decrease in the ‘scare’ factor, however, does not take the game out of the horror genre.
Overall we will have to see how Visceral Games implements the co-op campaign, and how well it works throughout the whole game. In the mean time we can only speculate, but lets hope that the game lives up to its hype and that the co-op feature proves a success.