ABM Command

Although the graphics are simple, it's a pretty entertaining game for the most part, although similar to many others produced around the same time. Basically, if I remember it correctly (It's been a while since I played) you control the bases at the bottom of the screen and try to defend them from incoming missiles and the like. It'll keep you busy for a few minutes, depending on the length of your attention span, but it's not too difficult to figure out.
As the game continues, the missiles will start falling faster and in larger numbers, so it does get more difficult.

Since you only have a limited amount of ammo with which to fire at them, it does get a little challenging. In the more advanced levels, some of the incoming missiles even break apart into three separate missiles, sort of like a hydra's head. You try to cut it off and it only makes more of them.
To fire your missiles at the incoming bombs, you have to click the screen where you want it to go. But you have to think it out because your return missile will take a little time to get to where you want it to go so you have to account for the amount of distance that the incoming missile will have traveled in that time before you click. There is nothing worse than sending a defending missile up and having it miss the incoming missile only by pixels and having said incoming missile land and destroy one of your bases. Talk about frustrating.
When you lose your base, or city, or whatever that little blob on the bottom of the screen is, you lose it for good so be careful, it doesn't regenerate or anything. The game will end when all of your bases are destroyed and once one gets knocked off, it gets even harder to defend the others so everything sort of snowballs until you reach "Game Over".
I remember playing this as a little kid and it was always fairly entertaining. It is one of those games that, although not having a two-player function, can be great to compete with your friends over to see who can get the best score. If you have time. And nothing better to do. And, you know, no better video or computer games to play at the moment. Once again, this isn't a bad game, it just, sort of can get old after a few rounds.