Windows 3.1 has never been a gaming platform. It was simply too slow and unstable. There were of course exceptions. Most of them were turn-based games requiring much thinking. And there was Win-Doom as an action game. But that's it. Almost. One game which showed one possible way to work with Windows is almost always forgotten: Metal Marines.
Most Windows-games tried and still try to cover the OS their running in. Mindscape chose a different way and even proudly used many Windows-driven options. That becomes clear at once when looking at the game because it runs in a window. Not only in one, but in several windows. Each contains something different. In the two main windows, a landscape can be seen. These are the islands the battle takes place. Each player owns one island/window. Here he can build structures like a HQ or a radar station, offensive weapons (missiles, Metal Marines) and defensive ones (Anti-Air Missiles, Bunkers, Metal Marines again). But the enemy only sees the landscape, as long as he doesn't scout it, he can't see the other's buildings.
The goal is now to defend you own command centers (you have three of them) while destroying the enemy's. To build weapons you need money which flows in all the time. Still you'll never have enough of it. When you've built a missile launcher for example, you simply use drag & drop to attack the enemy's island. Then the missile will fly over the window's border into the other window and (hopefully) explode on the ground. If you're not so lucky, it will be shot in the air by defensive missiles. Using Metal Marines works similar, only that they are ground units.
Against each possible attack, there's a defense. It's not overly complex, but that would only hurt the game anyway. Even though it's very simple (just ground/air attacks), you still have to plan a thought-out defense to withstand the enemy.
For single players, there's a campaign with slowly rising difficulty level. But it's much more fun to link two computers and battle another human. Only then the emotions will get really high...