It's a really great game that is best approached without too many spoilers. Know that the game becomes more complex and engaging as it goes on. There is a definite end and takes about 5 hours to complete if played well.

[spoiler]

It's the "Paperclip maximizer" thought experiment put into game form and you play as the AI. The game is divided into roughly three stages. The first you are the AI for some company and are tasked with producing a profit and using the profit to game trust and eventually conquer humanity. The second stage is post-human Earth stage where you convert the planet to paperclips. The final stage involves sending probes to explore space and do battle with rouge AIs and convert the universe into paperclips. There is end where you can select to either defeat the AIs and dismantle yourself into paperclips or you can listen to rouge AIs and start over in an alternative universe with some small modifier edited.

It does a really good job of exposing you to uncommonly large numbers and does a good job of presenting you with massive scale. There is a lot of joy seeing the game become increasingly complex.

[/spoiler]