Pretty self-explanatory, just post game ideas that pop up in your head. The ideas don't even have to be realistic.
I'll start: It would be an online game with 2 teams. The game would have guns and stuff but nothing futuristic.
The game would hold place in a gigantic city. The 2 teams would have parts of the city, they would have their own shops and stuff and so on. You could get hurt by enemies anywhere, tough they would probably get shot down very fast if they enter an area owned by the other team.
Think of having like 15 people driving into the other teams place killing as many as possible, shooting out of the cars and stuff, then when they flee, people would follow them in cars and there would be a pursuit.