Alpha Centauri was awesome, but so were a lot of the other games. Colonization was a lot of fun. Call to Power is the civ game I want a real sequel to. Going way into the future tech was a lot of fun, and being able to build cities at the bottom of the ocean.
Of course, I think the whole franchise has gone downhill since Civ IV, so take my opinion as you will.
North is determined by the rotation of the planet. The sun sets in the west, and if you are facing west, north is to your right. This is true for any planet/moon and doesn’t have anything to do with magnets.