It's pretty much what I expected, which is a good thing I think. n.n
I've got a medium-range machine (it was a gaming machine although not a super-high end one and it's a couple years old) with a NVidia 760 Ti, and it runs decently on medium settings. Which are probably the lowest possible settings because it doesn't let me change them. o.o; But it still looks pretty. n.n I saw a little bit of the half-second hitching that people are complaining about right at the beginning but it seemed to go away pretty quickly and didn't come back. Then again, I'm usually satisfied with lowish framerates and if it's dropping to 20 frames per second (the other thing people were complaining about) I probably just didn't notice.
I'm mentioning that because No Man's Sky has the WORST FAN BASE EVER. They were making death threats over the 3 day delay. They swamped Steam with negative reviews over the perf issues. OMFG what is wrong with these people?
...I am running into a persistent memory leak or something that makes the game slow to a crawl after 90 minutes, so the perf issues are real! I hope they fix them! But they're not the unplayable disaster that you'd think they were from what everyone was saying.
Aimless exploration seems to be the main activity, of course. Every planet has scattered monoliths that teach you alien language and outposts with random events (usually, multiple-choice quizzes in an alien language that give you a blueprint for something if you get it right), and then lots and lots of wilderness. Scattered treasure hordes. Giant mineral outcroppings. Alien life forms that are usually peaceful but there was this one planet (I named it 'FakeLake' because it had these blue patches of dirt that I thought was open water from orbit) where all the animals wanted to eat you and it was SO ANNOYING because they'd dodge and were hard to hit and then the sentinels would come in to protect the poor, precious flesh-eating monstrosities and...
...I probably should have just left that planet right away, honestly.
So, yeah. The different planets seem different -- some have water, some have caves, some have cliffs everywhere, some have flesh-eating monstrosities, most of them are toxic or radioactive or boiling hot...
But they're so big! And there's no way to get a hint as to how to get back to somewhere that you left behind. If you launch from a planet and fly around in space for a while and then go back to the planet, the odds of finding that outpost with the shop that lets you sell your loot are... not good. I wasn't able to do it, anyway.
So, yeah. It's fun, as long as you like aimless wandering and looting tiny 'dungeons' and mining. And occasionally running away from flesh-eating monstrosities.