Defeating Alien Troopers:
Hold R1 and run around them, shooting them
with the laser. If they are in a group, 
they  usually will not be paying attention.
Just stand back and shoot them in the head.

Defeating Alien Spiders:
Stand back, fire one secondary rocket 
launcher attack, a grenade (secondary 
machine gun), and finish it off with a laser
in the head. Be careful of the small ones. 
Stand far away and blast them with the 
machine gun.

Defeating the Boss in the Alien Base:
After Dr. Carter gets captured by the aliens,
you must make your way through mazes and
buildings to find her. When you do, her 
father, who has turned into an alien himself,
sends a war drone after you, The best way to
defeat it is to destroy the laser arm on the
left, followed by the one on the right. Every
now and then, pick up the items lying around.
Once they are gone, destroy the Drone. If the
laser arm starts to fire at you, or the drone
brings out its machine guns, just press 
Triangle to use your shields.


by unknown