Imagine yourself that you are in middle of ocean, but the ocean is 3cm deep only. everywhere you look around is water and water only, and there is nothing to do but just walk or jump, you can't even swim. You occasionally notice there is something new in the water, a different type of shade of ocean bottom maybe, maybe a bit different type of seaweed every 1-2km of walk. At first you might think that there might be something different out there, and its just the spot you were deployed is boring. Maybe there is a deep water with fish, sharks, treasures and submarines ahead.
But as long as you walk you discover that its the same everywhere, same 3cm shallow water, crashing loneliness, boredom and nothing more.
Thats how No Man's Sky feels.