I like Left 4 Dead but am far from obsessed with it like most of my friends are. I was wondering the other day if the enemies in the game were anything other then zombies would everyone still have been as excited or in love with it? I don't want this to come off as an accusation or a downfall of the game valve is a great game studio with a loyal fan base so maybe I am wrong. Still I feel like zombie love has a lot to do with it's success.

If there weren't any zombies then many aspects of the game would have to change to fit.  Left 4 Dead is great because of the zombies, but also for the 'realistic' portrayal of what the zombie apocalypse will eventually look like

You mean the 28 Days Later, they look like zombies, but they're not really zombies, zombies?
 
Wait, what if this was a 28 Days Later game? Then to answer you question, FUCK YES!

now that i think about it, it would be better if it was werewolves intead....

left 4 dead wouldn't work without zombies.  What, are regular people supposed to run at you and attack you for no reason?  It's called, "Us 4 Mugged"
 
you can't have Left 4 dead withouth the zombies.  Otherwise it would be a regulrar first person shooter with people shooting at you

I'd love it much more if it was baby mutants instead.

It wouldn't be Left 4 Dead without Zombies.

Well, what would replace zombies? I can't imagine anything else that would work. The whole appeal of L4D, at its core, is teaming up and killing a bunch of zombies. It does this well, so I don't see a need for it to be changed.

I mean they could always do the classic out in video games of aliens or even hell beast and still keep the atmosphere, game play and units the same. Now I'm saying those three things are really what makes the game I just feel like if it was aliens it wouldn't have the same following it has.

I might've done, but the whole 4 people against an on going horde of zombies is what really sold me.
Along with this trailer:
 

" It wouldn't be Left 4 Dead without Zombies. "

" @animateria said:

" It wouldn't be Left 4 Dead without Zombies. "

*echo*  Still, there really should be more mass vampire/werewolf fighting games.  Or, there enemies could be armies of my little ponies. Or *zombie* my little ponies. Think about that. "

" If there weren't any zombies then many aspects of the game would have to change to fit.  Left 4 Dead is great because of the zombies, but also for the 'realistic' portrayal of what the zombie apocalypse will eventually look like "

" @FlamingHobo: Looking at the video I find it amusing that Bill's design never changed..."

I wouldn't mind fighting a few pirates.

What you mean like "Left 4 Ice Cream", Ice Cream van chimes, you and three friends must make it to the Ice Cream drop-zone before hundreds of kids buy it all and you left with a few Ribena ice poles? 
 
Yeah, I'd probably still buy it.

I would prefer if you hacked your way throuch armies of penguins/ chimps.
Either that or Noes Edmonds  *shudders *

If the zombies were replaced by Pokemon, I would have bought two copies of Left 4 Dead instead of just the one I have.
 
Now the issue becomes whether the Pokemon are zombies or not.  I wouldn't care but seeing zombie versions of Pokemon would be a little weird.  I would rather have a collective Pokemon mind error that caused them to attack humans in hordes.  Boom!

The games formula and substance is what matters.
 
If I was playing against wild chickens but it was the same exact game as L4D I would buy it.

You know, I like that idea of shooting hundreds of mindless children that are running at you...

No, it would be terrible.

" left 4 dead wouldn't work without zombies.  What, are regular people supposed to run at you and attack you for no reason?  It's called, "Us 4 Mugged"  you can't have Left 4 dead withouth the zombies.  Otherwise it would be a regulrar first person shooter with people shooting at you "

Could been robots, coulda been ninja, coulda been wildabeasts. If it played the same, and gave me a sense of tension and teamwork that it does, I'd like it all the same. 
It's not like they'd have to change the story: "Army of santa clauses run wild, ACTIVATE!" 
 
I'll shoot just about anything a game tells me to.