Well combat is just based on how you designed your ships(yes you design your own ships).
The better the ship, the great chance you have of winning the fight.
Planet invasions are alittle more interesting.
You pick various option on you wanna start the invasion, things like gassing the population, spread propaganda etc etc.
Each of these will give you a special boost for the common battle.
There your invasion force(numbers depends on the size of your transport ship which you also design) against a certain precentage of their population.
You then roll a dice that decides advantage and disadvantage and battle starts.
But overall combat is nothing special at all which is really the only con in the game.

The rest is superb really.