I won't go over everything as this has been done to death, but Sean was asked straight questions such as "can you play with your friends" and his answer was "yes" but as we now know this was not possible and they knew it but didn't tell people who had preordered the game.
No landing on asteroids, no ringed planets, no proper solar system orbits, no day/night cycle... the list goes on.
Yes, they've released a lot of content since launch but it doesn't excuse the fact they promised certain features which were not delivered. If they had to cut stuff that's fine with me, it's the reality of producing a game, but they should have let people know so they can make informed purchasing decisions.
Old reddit post but list of stuff is here: