This is my opinion, but an open world, aka “sandbox world”, game only works if you have something specific. Whether you like GTA or not, the sandbox world does indeed work.
For a game like Ghostbusters, it is a little bit trickier. Sure it might sound good on paper, but it might not work in practice. How can you make driving from location to location fun enough so that people want to play it? Previous driving parts in past Ghostbusters games have been not so successful. Look at the videos by Angry Video Game Nerd for better details.
If they can make it right, I guess it could work, however I do remember in one interview about ghostbusters that is found on
Xbox.com I believe that talks about a mission where you actually escort the Ecto-1B down the street while fighting ghosts. Not sure about the details in particular, but this is probably closest you will get.