9 planets total to explore for now, with tons of items to craft and use towards an end-game goal. After the end game you can still explore and create/build more.
The Nov 15 update is also adding a creative mode and the ability to use "dedicated servers" which i'm guessing is like how Steam used to allow people to run their own servers for Halflife/Counterstrike and maintain your own persistent world?
Been watching 2 Youtube streamers for a few months now, they even have some emergent multiplayer activities, where you can start a new save with friends and try to build things together.
Haven't been this excited over a new game since NMS launched.