Someone at Reddit devoted a lot of time to research trailers and gameplay features which were promised but aren't included. The account and post are deleted today, but can still be seen here
https://web.archive.org/web/20160816191001/https://www.reddit.com/r/NoMansSkyTheGame/comments/4y046e/wheres_the_nms_we_were_sold_on_heres_a_big_list/

I resisted the preorder when it came up on GOG, and from what I see at that link it was the right decision. What's left may still have worked as a 20 or maybe 40 bucks "indie early access" title, but it appears they are selling half of the promised content/gameplay at full price.