Type the words before they reach the bottom!
As you might guess, going for an open world game in a jam is not the greatest idea because how much of a time sink it can be. But the world actually ended up being pretty nice! Race the the intel points marked on the map and return the base. Collect money as you complete missions that can be spend on upgrades! The game even has upgrades for the car, lots of different missions, and a local high-score system for each of the missions.
Here is a Tower Defense game made in Unity. I wanted it to be easy to make changes to the balance and create new content (tower and waves). Therefore all the towers and waves are read from an easily changeable XML file where you can specify any number of towers and waves you want.