The more long you survive, the more it becomes harder !
(Speed increased, more asteroids spawning).
And it's inifite !
You have to shoot the maximum amount of asteroids to make the best score.
Note that the more it's difficult to shoot an asteroid (by its speed and its size), the more you gain points ! ;)
You've got an health bar and you'll see that the more bigger is an asteroid, the more it will hit you.
Keep in mind you've got some shields and you can use these with the right click.
During the game, there's some chance to get shields, lifes, repairs and of course, spaceship upgrades !
And that's all folks =D
Good luck amigo !