They are very different. X4 is more of a grand strategy game where you need to build up your empire. I really like how all the resource production and manufacturing works. You can't just buy ships. They need to be built. From parts. That need to be manufactured and supplied. If you want to beat an enemy empire then you can attack their supply lines and they can't produce new ships.

The game starts off much like Elite, just you flying around in your ship. But by the end you usually just sit in a chair pouring over the map and issuing commands while your hired npcs do the actal work.