Sid Meier's Alpha Centauri

The Good
Science fiction turn based strategy. Wow!

The entire package (UI, game events, sound effects) is superbly integrated resulting in a game that is so immersive you lose all track of time.

The user interface is intuitive (at least to those used to these type of games), there are multiple ways to accomplish the same action so that as you become more familiar with the game you learn shortcuts and move more quickly.

The Bad
Learning curve for technology tree.

The Bottom Line
The best single player strategy game available today. Not for beginners.