It's a turn based space empire strategy game focusing more on the pure strategy aspect rather than surround sound and pretty lens flare graphics and such.
It's run directly from the windows GUI and to the untrained eye looks rather 'lame' compared to other games. But for a person who enjoys playing space emp building games such as MOO2 or Ascendancy (which is free to download from the underdogs site, as is the original MOO) it's quite immersive.
Stars! is more from the perspective of an intelligence report style of play than you actually playing as the 'god'. Fleet battles can range into hundreds of ships for all sides involved in a single battle. The game interface looks something like this...

Oddly enough I found this screenie laying around in the tap site folders. One of the other Tappers must also be a stars player *shrug*