all games are not created equal

(I mainly wanted to check out the category function of comparisons now :D )

Ghostbusters and L4D both feature terrific voice acting.  Ghostbusters has the advantage though, mainly due to the actual actors of the movies reprising their respective roles in video game form.

Dan Akroyd and Ernie Hudson stand out to me with their voices.  They're instantly recognizeable, lively, and really help bring the characters to life.  Harold Ramis is still great with his technobabble.  I was sadly dissapointed with Bull Murray, who I anticipated to be a standout.  Bill Murray sounds very quiet and very very sleepy the entire time.  Too bad.

L4D's characters also have great voices and they all sound lively and energetic.  I think the stand out is Francis though, with great lines such as "Nice shot Bill, that was my ass!" and the infamous "I hate elevators/subways/sewers/hospitals/trainyards/small towns/water/helicopters/etc etc etc" . 

While both are great, Ghostbusters still has the advantage where your character doesn't say anything, or even has a name.  It's perfect, as it doesn't at all get in the way of the vets talking amongst themselves.