The strongest point that makes Aliens vs. Predator series what they are is the unique gameplay.  Three way slaughter matches between three different species.  And Humans being what we it is sometime a fourway.  But below gives some detail into each species, along with thier strong and weak points.

::: ALIENS
+ The Aliens are the most aggressive species in the game.  They move with lightning quick speed, clinging to walls and tearing a human or predator body into peices with razor sharp claws, inches long teeth, and a stunning spur from the tail.  There are a few different "races" in these species:
+ RUNNER
+ DRONE
+ PREDALIEN
+ PRAETORIAN
+ QUEEN

::: PREDATORS
+ The Predators are basically some sick bastards.  They get pleasure from ripping off heads and just plain killing things.  These beasts walk upright and can take alot of bullets.  Thier technology allows them to bend light to become invisable, therefore becoming some pretty tough opponents.  These species are harder than hell to kill, but are weak to fire.

::: HUMANS [Marines / Corporates]
+ Well, who doesn't root for thier own species?  The Humans are armed to the teeth from Pulse Rifles to heavy Rocket Launchers and Miniguns.  Thier weaponry is thier strength, having no extra physical powers like the other two species.  It doesn't take too much to kill a Human but watch for the deadly weapons in the right hands, ones that know how to aim.

This isn't too detailed, there will be more coming, but it's good for now.