The basic premise is for each player (2-4) to have start with a basic base, a few personnel - soldiers to fight, workers to build projects and scientists for research project. Each would start with an income as well as immediate finances.
UFO will pop up, players would need to intercept and shoot them down with fighter jets, then send in soldiers to grab artifacts.
Taking these artifacts back to their base, players would research them to gain money and special abilities that would make certain things easier, and give access to new buildings.
Eventually a game end event will occur, such as a mother ship showing up and players would have to work together to defeat it before checking who has made the most points, or something similar.
One of the interesting ideas that came from this exercise is the building / research mechanic: each project would start with a certain number, higher for bigger complexity. Each turn a worker/scientist on the project would place a counter, once the number is reached, the project it done.
Placing more workers would shorten build time, but increase cost, making it an important choice.