If you bought No Man's Sky on Amazon, Steam or the PSN network, you should be able to ask for a refund, regardless of how long you played the game for.
Players on reddit have been successful getting a refund on Steam, even though Valve usually only allows refunds if you’ve played the game for under two hours. Fans who bought the game on the PSN who put upwards of over 50 hours into the game, also claimed to be able to get a full refund from PlayStation customer support.
To get a refund, just contact whichever provider’s customer support you bought the game from and how you truly felt about the game.
If you haven’t enjoyed No Man’s Sky and felt that this wasn’t the game you were promised, get your money back.