More details from Famitsu/etc. I translated for CR the past few weeks:
- Case 2 is basically a sequel to the first game's 4th case, and in fact takes place between DGS1-4 and DGS1-5.
- Viridian Green (victim of DGS1-4) and the two mysterious men who made cameos in 1-4 have major roles in the second case.
- The third case jumps back to the present day and is about an explosion at the World's Fair during a teleportation experiment.
- Gina returns as a detective-in-training.
- Eshiro and Takumi have stated many, many times that they plan to wrap up all the lingering mysteries from the first game with this one. They aren't ruling out a DGS3 but it would depend on this game selling well and Takumi having a good idea for one.
They're releasing recap videos, though the only one out so far seems pretty basic. They'll probably have a good amount of recapping in-game as well.
Game's out August 3rd in Japan.