Even though it was made to prolong the PSX's lifespan, it's still a good game.
You're playing as Vaughan, the Lieutenant for the Resistance Force, a group of humans keen on saving they're planet from the unwelcome guests. Vaughan has been made into a cyborg by the Resistance, (a human-machine) in order to fight these aliens who are invading from everywhere. You'll start out with some alien blade as a weapon to fight the cyborgs and aliens, but after you've finished the game you have used everything from Rocket Launchers to Laser Rifles.
There's lots of cool things in this game. One of them is that it can sometimes get pretty scary. Sometimes you're walking around in the city when all of a sudden an alien comes at you and really scares you. Another kind of creepy moments is when you're in a factory where the aliens are performing all kinds of sick experiments to the humans.
Another cool thing is that everyone of your weapons have two attacks. For example: the machinegun can aside from shooting regular bullets also shoot grenades.
And the third cool thing is just that this game is so well made it's just fun to play. It has of course some problems like frustrating puzzels for example, but that doens't ruin the game. C-12 Final Resistance proved two thing to me.
1: Even though the PSX hasn't as much power as the PS2, it still proves that it has enough power to make an exciting game.
2: Even though the concept has been made a million times, when done right it can feel pretty new.
If you like actiongames, I recommend C-12 Final Resistance. It might not as good as Metal Gear Solid, but it's still a good game.