Left 4 Dead 2 is not a terrible sequel because it doesn't have as many horror elements as Left 4 Dead 1. Left 4 Dead is inspired by horror driven zombie movies like Dawn Of The Dead and 28 Days Later, while Left 4 Dead 2 is inspired by comedy driven zombie movies like Shaun Of The Dead and Zombieland.
(Edited)
It's nice to see people understanding this between the two.
^ This
I enjoy both. L4D1 has a more serious tone while L4D2 has a more light-hearted tone.
I love both, but I definitely prefer L4D2's more comedic tone.
L4d2 is more comedic, but it's not like L4d1 is devoid of humor. Both of the games are satiracle toward the zombie genre as a whole. The sequel is definitely more light hearted in its approach, but it still manages to take itself seriously in much of its dialogue. Personally, I always saw Zombieland as an influence of the first game.
Oh yeah L4D1 definitely has it's comedic moments and L4D2 has it's serious moments too.
I was thinking about this more and I take back what I said about Zombieland. There was so much zombie media by 2008 to influence that movie, L4D1 doesn’t really come close and the similarities in L4D2 which came out a year later are pretty obvious. I think the increased satire of the second game made Valve seem more self aware. Killing Floor also tried going down this route, but I don’t think it really benefited the sequel at all. They just turned something terrifying and disturbing into something silly and quirky