Hmm... what about making a cop game(using an X-Com type game engine) that takes place in different Epoches in time? ie. You star out a a modern-day Police Swat and Emergency Task forces and over the next so-many years(your whole term as police chief) or so you constantly upgrade your equipment and armour, receive funding from the city, etc... and eventually you'll end up with those some really cool futuristic-type weapons, armour, vehicals and other equipment. Also the terrain could change too. Modern-day(1990-2000) street lights and sidewalk tiles to really out there Jetsons looking glass or steel sidewalk tiles, etc...

Lots of things you could do there. Dialog triggers, crime indicator screen and police radio type of alert for the "global" screen. You could make the global screen some kind of 3D ray-traced map of a randomly generated city. The city could grow in size as the game goes on too. Eh... I'm an idea man, what can I say.

BTW, I found that X-Com 2 wasn't that bad. Basically the same engine(which is why I liked it, I guess) and the underwater element was ok too. Only thing is that the difficulty got too hard too fast, I think.

X-Com: UFO rocks!