Originally posted by mlk.mn:

Built a base and a boat. Is that it?

Sandbox games.

It is where you play on your own pace, and, basically, "create your own story". All that is possible because developers are not focused on developing the game in a "pulling you by the hand", movie manner, and instead, provide you with many interesting ways to interact with the world, many physics features and random content, that you might easily miss if you're not looking for it.