This is a prototype of a game I am currently working on. Its the farthest I've ever gotten with a game before so take that into consideration.
I decided to turn the classic alien defense game on its head. You play as an invading alien spacecraft intent on destroying a peaceful city. Each time you play, the city is procedurally generated.
Add more buildings and houses.
Add more weapons such as a lightning arc (almost done), guided missiles, and ground drones.
Add lakes and trees.
Scale buildings upwards toward the most densely populated point, in effect creating a "downtown"