I think practically, and even story-wise, we'll never see a free-roam Ghostbusters game like the recent
Spider-Man and LEGO Spider-Man/Marvel/DC offerings... Even at it's videogaming height, the developers of GB:TVG opted for limiting the free-roaming capabilities to a few large levels (predominately if not entirely because they didn't have the budget and staff to achieve something larger).
Then there's the issue with the concept being in-spirit (no pun intended) with what we've seen in the Ghostbusters media to date: every bust the guys have been on has been unique from the one before, even if they have multiple cases with Class 5 Free-Roaming Vapours... back-to-back, each ghost had had a unique look, story, and motivation... Something you just wouldn't be able to do with the gestation time and space limitations of even a modern Xbox/Playstation game...
Which would ultimately result in many of the "random" ghost encounters in said game becoming repetitive because you'd encounter the same group of ghosts, or individual ghosts, packaged with the same responses from the NPC civilians.
Ghostbusters: The Video Game may've felt contained in a box compared to other games, but in being contained in that box, I think it allowed the developers to add extra focus to the characters, and to make sure we didn't get too bored by the ghosts we encountered... Even when they were duplicates.