It was in the works forever, but the roadblock was Bill Murray.
Then it was going to be an animated movie that he would supply his voice with (he agreed to that, but not live action)

Then that turned into 'lets make a game'

I'm wondering if they did the voiceovers for the game and scripting they convinced Murray to agree to making a number 3.
I'm assuming the conversation went something like this:
"Bill, your last movies suck, we know you need the cash...so... derpppp"

Originally the movie was centered around the old ghostbusters training the new group,
being Chris Farley, Will Smith, and some other names were attached. Recently names like Steve Carrell and the Judd Apatow crowd being the new guys.

The original story was based on a negative New York (being Hell)
Ya know, dogs and cats...living together... MASS HYSTERIA