I never played Dead Space 1 or 2. I'm terrible with horror. Steam says I've played Amnesia for eight hours. Lies. Those eight hours are from a friend playing it, or from me staring at the title screen.
Dead Space 3 was a fun co op game. Probably the only way I could stomach any horror game is by playing with a friend over the Internet, or with a friend yelling at me while we're sitting on the same sofa. But there was a point in Dead Space 3 where the game just breaks. The weapon customization systems, while fun, are horribly unbalanced. By the end of the game, I was wielding two dual-rocket launchers with blast shields.
There's a point in Aliens where Ripley duct tapes a flamethrower to a rifle. It was just like that moment, when I crafted those two awesome weapons of destruction. The moment you knew that nothing in the universe could stop you. Maybe that's what the writers were going for? Where it's revealed that Isaac is the true monster? I don't know. But at that point, it was no longer Dead Space. I was Space Rambo.
Still, scary stuff is fun with friends around. Especially Dead Space 3's co op, which I think it nails perfectly. That elevator ride with Carver. You know the one. That was great. Especially when I was playing as Isaac.