A great addition to GOG. You can do so much. You will defend your home planet, wage wars of conquest, intrigue in the capital planet (no standard troops allowed), and help in the war against the aliens.
You get resources from planets you own. You can use them to create new units. Special units (straight from the tabletop game) such as space infantry and recon infantry are very fun to use (cannot remember their exact names in the game, but you can figure out). Space infantry (marines) can attack starships in space (by boarding them), as well as landing on a planet (but for getting spaceborne again they must reach a spaceport). Basically, space marines are super expensive but can defeat practically anything on the surface of a planet. Although you best save them for something that is really worth it, as they are truly expensive You better take good care of them. Also, once on a planetary surface, they do not move fast. On planets you will do better with cheaper regular units for sustained combat.
Recon infantry can perceive over a long distance. They are very useful as well.
There are spies that you can use in the capital planet. And armor, artillery, more infantry, and so on. You can do whatever you want, and each planet is a world in itself. The game is vast. Resources will be scarce for everything that you are to accomplish