The Interceptor

The aliens are here, and they're hellbent on razing city after city to the ground, by indiscriminately dropping bombs from orbit on everything that stands. The only defense against the extraterrestrials' obvious dislike of Earthling architecture is the Interceptor: a flying vessel armed with rockets, which launch upwards to take down the trigger-happy UFOs; and side guns, which fire shells to dispatch the descending bombs.

The Interceptor proceeds from city to city to repel the waves of alien attacks. It takes damage from direct hits, and has a finite supply of ammo, but can be repaired and resupplied by setting down on a landing pad. To clear a level, all enemy ships must be taken down; besides conventional bombs, the aliens pack two more dangerous types: nukes (red) which can instantly level a city, and fusion bombs (blue) that destroy anything in the air if they detonate - including the Interceptor.

Points are awarded for destroying alien ships, but every fired shot and every object destroyed by the aliens will detract from the final score. The more buildings (and trees) left standing, the better.