While the previous Disaster Reports took place during or immediately after a disaster, Kujo said, Disaster Report 4 begins about a week after the event that wrecked the city, allowing players to see the social effects (like discrimination causing strife in shelters) and even recovery efforts following a catastrophe.
Toward this theme, you would also have been able to travel with a variety of different characters you meet in the city, as opposed to the single partner of previous games. Since the emphasis was no longer on fleeing the city, you could even visit the same location later and see it partially rebuilt.
All of this sounds really interesting, until we remember that it was canned. Kujo said that it wasn't the earthquake that ended this game, but Irem's slow progress in completing it. Kujo has since left the company for a new developer, Granzella.