An exciting game Aliens verses Predator, by Sega.
In this first person shooter game, you can choose to play either a Colonial Marine, a Predator, or an Alien Xenomorph.
My favorite character is to play a Predator, you can render yourself invisible, to a marine. Then sneak up for a quick kill, they cannot see you, but can hear you make a noise.
However, the aliens can see you, even if you are invisible.