Each kind of Robotron has a different way of attacking you and also different point values. Points are also scored by destroying the missiles that they fire at you, by destroying other enemies that appear during each wave and by saving humans. Hulks are indestructible and will kill humans as they approach. Your blaster will only halt them as long as you are shooting them. Obstacles such as Electrodes in your path can be removed by firing at them with your blaster.
Humans are worth an increasing point value.
The first human scores 1000 points, the second is worth 2000 points and so on until the point value reaches 5000. The point value will remain at 5000 for all the remaining humans in the same wave. When the wave is completed or you have been killed, the points awarded for saving another human will be reset to 1000. Your score will be unaffected. The default difficulty is 5.