Solo survival (in single player) and kill confirmed (new multiplayer game type) are incredible.. If you haven't tried it already, you're missing a ton of fun.

Worth buying just for spec ops. Even if you don't touch multiplayer, single player and spec ops alone are worth the money.

Although it might not be great as it's predecessor (in many aspects l4d2 is way better), I absolutely recommend this game to everyone regardless of their age (7 (6 year olds or less should play xbox/ps3 version) - 777, not fair if vampires are excluded since they play versus in real life too lol), gender, ethnicity, religion (if your God is against violence and playing such games, please ignore him, Left 4 Dead series are something you really dont wanna miss, cause you only live once and burning in hell is certainly worth it if that's the price) or whatever. If you already dont have the game, you're missing out a great experience. As for me, I already enjoy both Left 4 Dead's, I don't believe in God and when I die I'll just respawn (like in a video game) on the other part of the planet (hopefully China, Taiwan or Korea for prosperity sake lol) and guess what? I'll continue killing y'all in video games again hahaha. Perhaps even in Left 4 Dead X.
Call me crazy, but I meant what I said.