Game Rules:
Level 1: Kill 40 Enemy Aliens without getting hit before they reach the bottom of the screen and pass your fortifications.
Level 2:
Afterwards, kill the UFO by hitting it 100 times without getting hit by its rockets before it reaches the bottom of the screen
and passes your fortifications.
Bonus Points: You will receive bonus points if you win depending on how many shots you fired (time your shots, don't spam space).
Bonus Point System: 140 Shots Fired or Less: This means every shot you took was a kill and earns you a bonus of 5000 points.
200 Shots Fired or Less: Not perfect, but will still earn you a bonus of 3000 points (Most commonly achieved).
250 Shots Fired or Less: Shouldn't need to take this many shots in the first place, but, luckily, it still earns you a bonus of 1000 points.
More than 250 Shots Fired: You'd be lucky if you win the game; no bonus points.
Win Condition: Kill the UFO