Battlestorm

A top-down space shooter that was different from most others at the time in that it did not just scroll continuously in one direction, but could scroll at different speeds in all possible directions on the X and Y axis, on the player's whim.

The game takes place above the surface of a ruined, devastated planet: each level starts within a large area, in which your ship has free movement. Avoiding surface hazards, such as auto-aiming turrets, the goal is to destroy enemy spacecraft that hover around the large area in groups. Each wave of attacks is followed by a bomb-dropping mothership, which you must hurry up and destroy before it moves off the playfield, in order to proceed to the next wave; the last mothership gives way to the boss - a gigantic spacecraft that will chase you around the playfield. Beaten it? You are transported to a short section of standard shooter fare, where the screen auto-scrolls vertically, at the end of which you face a final monstrosity. This ends the level - on to the next one.

Absorbing enemy fire will deplete your power, while collecting power-ups and destroying turrets can bring it back up somewhat. At 0% power, the game is over - although you may get an option to continue, based on how far you got.