6 difficulty levels:
* Beginner : no gravity, no fuel
* Gravity : no fuel
* Limited fuel : standard
* Darkness : sector lights are off regardless of power station status
* Three lives¹ : presumably number of lives capped at 3 or even extra lives have been removed.
* Motion sickness¹ : presumably all levels spin and not just the late ones

¹) Unlocked somehow.

There's total of 80 levels ("sectors"), ~10 last of which spin around at varying speeds.

The story is about you going in to the star hulk Icarus in search of its power core.