Left 4 Dead is one of the greatest zombie games ever made. This isn't due to the awesome and addictive cooperative gameplay, but due to DEAD ZOMBIE BUTT. No Mercy - Chapter 4 is the best level out of the whole game for this simple reason.
It's silly to think that everybody will be fully dressed when they become infected, so why don't more zombie-themed games feature dead zombie butt? Is it because developers are too scared to feature nudity in their games? If so, that shouldn't be an issue. The following is a scanned image of the ESRB rating for Left 4 Dead:
Notice anything missing? Exactly. Nowhere does it mention nudity, even though there are quite a few dead zombie butts in the game. Sure, showing a couple of buttcheeks is no longer a big deal nowadays. You see them all the time on TV, even in cartoons and such, but those shows don't get as graphic as Left 4 Dead. In Left 4 Dead, a slaughtered zombie can fall down and be positioned in all sorts of different ways, and on multiple occasions, I have killed the gown-wearing zombies in such a manner that they land with their ass up in the air, Johnny Sasaki-style, but this time, nothing is blurred out!
Valve has always been a pioneer in the gaming industry, and dead zombie butt is no different. Hopefully in the future, other game developers will wise up and realize how excluding zombie nudity is detrimental to their games. I'm sure Left 4 Dead wouldn't have sold nearly as well if it omitted such an important addition. Left 4 Dead 2 did so well because Valve ignored the controversy and continued to feature an abundance of zombie upskirt. The Spitters even wear pink thongs! Truly, they are a master of their craft, and I would love to see other developers take things further.