One of my favorite video games as a kid and I still play it to this day. I had the Super NES version, which had a simpler interface and additional music score versus the PC version. It also made use of the SNES mouse.
If you enjoy Sim City you will like this game. You start in the year 2090 on one of ten planets with a basic space colony already built up. While the game is open-ended, your main goal is to grow the colony and improve the quality of life rating to 100% through your management and actions.
One of the neat features of this game is the calendar system. Unlike many other real time strategy games, you don't simply plop down buildings. Each building requires a certain number of days to complete. Then, laborers required to produce resources from the facility are gradually recruited from your colony's population over several months.
Think of it like growing business and employee training process. For example: laboratories do not immediately start producing technology improvements; they must recruit scientists. So this requires some long-term planning.
There is also a resource management system with a simulated market economy. Build mines and chemical plants over ore and fuel deposits, respectively. These resources are used in building tanks and spaceships (more on that in a bit) or may be traded on the market. Of course, you will need to build warehouses to store the inventory.
Be mindful of your population's consumption of resources such as food. Overproduction sounds like a good idea at first, until it fills your warehouse space leaving no room for other needed resources. And if the market economy has no demand for food, you could be stuck with it for several months before you can sell it off to make room for other resources.
No real time strategy game would be complete without an enemy, of course! There are ten planets to choose from of increasing difficulty. Invest in spying grant to learn about the different aliens' location and cultures. Unfortunately, you don't get to see the alien base on the map, but they will send their own tanks and spaceships that move around the map in real time, causing all kinds of damage to your city.
But you are not without your own arsenal. Tanks and spaceships may be built to defend your base and eventually, launch an attack when you have built enough of them. Then there are purely defensive structures. Laser cannons can be quite effective, but are power hungry. You will need several power plants to power even a small number of cannons. Missiles are expensive and one-time use, but can be a life-saver.
I find it's more effective to sprinkle tanks around the perimeter of my base, and then launch a strike against the enemy when I have at least 90 or so. Spaceships are highly effective at defeating the aliens, and you only need a dozen or so to win, but they take an extremely long time to build.
There is also a science system in the game. It is not a tech tree like in Civ games, but seems to be linear. Basically, you build labs, which recruit scientists. Keep funding the grants every month, and eventually you will be given building improvements, better tanks, spaceships and other technology that raises the QOL.
The movement interface for units is rather clunky, but considering the age of this game it can be overlooked. The interface is NOT like Age of Empires in which you drag a box around units and right click to move them. Instead you must position numbered markers (you get eight of them) and tell each unit to move to that marker. Fortunately, you can instruct several units at a time (the game will find the closest units automatically). It takes some getting used to, but forgivable.
Some of the later levels can be impossibly difficult. It is still a fun game to pick up from time to time and see if you can beat the next planet on the list, or retry earlier levels with new strategies.