I cringe when I hear of somebody buying a computer game. It’s like paying for the privilege of wasting time. I can’t be too critical, however; because a few years back I was an avid game player myself. At the height of my time-wasting addiction, I played Age of Empires II for as long as ten hours straight.
The first is Glest. It is a real-time strategy game with game play similar to the Age of Empires series. Like most modern RTS games, it uses a 3D rendering engine so you are free to change your point-of-view by rotating and zooming the display. The more recent versions have added the ability to play with others over the Internet. Nice!
Another good one is Battle for Wesnoth. This is a turn-based strategy game and there is a bit of a learning curve. If your experience is like mine, the effort will pay off with a LOT of wasted time and possibly a stubborn addition to the game. Like Glest, you can play against the computer or other humans. Since it is turn-based, Wesnoth can even be played like a board game by several time-wasting humans huddled around a single PC.