I think you got them mixed up. The Single player was amazing, but I think you need to look past the normal shock horror that you expected of the first one. I think that this time around they wanted to go for a more psychological horror; maybe it was just me, but I found the kamikaze babies in this game to be extremely disturbing. Yes they were necromorphs and obviously its kill or be killed, but at the same time they were still SO HUMAN that they might still have some humanity left in them, especially since it's never really revealed how much consciousness one has after becoming a necromorph. They coo, they gurgle, they crawl,they even embrace even if it is just to get closer to explode, and I could never get over the fact that they just might still be a little human, still might just be a baby somewhere in that terrible body. Other things were good psychologically too, the atmosphere in some places was amazing, like the elementary school, and the sense of desperation was a lot greater this time around.
That being said, the multiplayer just seemed like a joke. In Left 4 Dead you already CAN play as the special zombies, so this just felt like a rip-off of that. Granted it isn't completely the same, but Left 4 Dead just seemed better, and I'd rather play that.