I used to play this one for PS1 at a friend's house.
It's a multiplayer FPS (You can play it single too, but it's SUPER HARD). You gotta defend Earth from a spider-like alien invaders. You got to choose between two Armorines: The male (Gold) one shoots slower but stronger laser weapons, while the female (Blue) one shoots faster but it's weaker. (Both are great, trust me).
You gotta work with your companion to go level by level destroying this small and giant spider creatures. Your main weapon got unlimited ammo but it's weak. The other weapons are really limited and the ammo is very low. Health kits are also super limited.
So, you gotta play smart.
I never got to finish the game because it was super hard, but we had so much fun playing it over and over with my friend.
If you, or the other player, dies in a level. It dies, permanently, so the remaining player has to finish the game alone if it can. And trust me, you won't. So you better play safe and take care of your partner so you both survive to the next level.