l4d/2 are not horror games, they are co-op shooter games with zombies. you could replace zombies with giant purple snakees and cookie monsters and it'd be just as scary.
anyone who says LSD is a horror game is wrong, as horror games are intentionally scary. LSD places you in a mindset where you are paranoid of something you don't understand jumping into your face, making you afraid. it was basically meant to be an adventure type game. it's like when you attempt to say a compliment and it comes off as offensive to the other person.