Strategy done right, even after 14 plus years X-Com holds up extremely well and still sets the standard for strategy.
Aliens are invading Earth, you must stop them. As the commander of X-Com you are in charge of building bases, managing finances, shooting down UFO's, recovering them, then reverse engineering and manufacturing gear to fight the aliens on their own terms.
Sounds like a lot? It is a lot. From budgeting to fighting you will be busy.
Combat is turn based, you position your troops and attack if you can then the aliens do the same. You start off with inexperienced troops but they get better as time goes on. The aliens are tough customers, there are several races with different stats and abilities and they are almost always better than your team.
The game can get a bit stiff at this point, there are many times where you take 1 step off of your troop carrier and are blasted before you can do anything. This is incredibly frustrating, but nothing reloading cannot solve.
Between fighting and deciding what to research the game never gets dull. Even the turn based strategy battles can be intense and exciting.
X-Com is one of the fines games ever made and should be added to your collection if you are a fan of the genre.