I think this is a exploration game, and has no real goals in it; I suppose you will have achievements, but will not be forced to get them.
Think of it like Minecraft: you spawn in a unique world, explore around and mine: this is your main activity in this game. But then what? You can either build a ginormous castle, or make autonomous machines with redstone, it's up to you. Space Engineer is quite the same, either build the most beautiful ship, or take down as many military escorts as possible, whatever you please.
In No Man's Sky, if a great diversity is achieved, you'll have achievements like finding a rare specie, hidden landscapes, and find out what are those "Tets" (a la Oblivion) for.
As always, great potential as a game, already beautiful game engine. I guess we're now playing the waiting game ...