Every time I hear the gameplay loop described, it doesn't sound fun at all. And it doesn't help that it's always a giant wall of text when a few sentences should suffice.
I'd argue that maybe also a lot of rogue-lites and survival games have a very dull sounding gameplay loop (especially if you don't disclose the actual amount (and variations) of loot, enemies, locations and other gameplay systems), but I think the "giant wall of text" bit is absolutely the number one reason why so many people have trouble figuring out what this game is about.
If they'd shown a half an hour of an actual, unmoderated gameplay loop (with all the glitches and rough edges of an early access game, for example) showing absolutely all (or most) gameplay systems early on (they've started doing some of it much later in the dev cycle, especially in relation to the marketing push), it would've been a lot clearer to most people. I'm not actually saying they
should have done that, as I'm kinda happy they didn't (although I might've preferred if they were these strange, esoteric devs with a cloud of mystery hanging over them), but if they did, it would help the marketing side of things. That's why I'm very interested in just how well it will sell despite all that, or will it really hurt its sales (but there won't really be a good way of knowing that for sure).
But yeah, for the folks that try to explain the game with long walls of text (including myself!), it doesn't have much of an effect (and I'm really not trying to insult anyone here, on any side of the argument).
No Man's Sky is a freeform first person single player survival/exploration rogue-lite space trading sim set in a procedurally generated universe (as in whole galaxies), with endless alien species to discover, battles to fight and money to earn, gather resources, upgrade your gear, suit and ship and discover the mystery of the center of the universe.
That's what you do.
How you do it... (which is what most people actually mean by saying "what do you do") well, that's something you can piece together by reading massive info repositories, watching some gameplay preview videos and make educated guesses, but because how info dumps and marketing's been handled, we'll really know the full breadth of the gameplay once the game comes out and there's been enough time to learn most emergent gameplay systems.