There's a reason why Gears of War derives a lot from this game.
The plot is sort of half-assed, and I don't really understand it, so I'll just say what I know. Apparently in the future, soldiers are controlled by people at computer terminals (called Controllers) who command these soldiers' every move. Some criminal mastermind hires a Controller and his soldier to go around the world, stealing nukes, framing countries, and attempting to start a world wide nuclear war. Bishop, the soldier, apparently has some blocked memories of his past and needs to find out more about it as the game progresses. It really makes no sense, and it just holds up the game.
The gameplay is a lot like Gears of War. You duck behind cover, pop up to shoot, and duck back down. Duck, pop up, shoot, duck again. However, unlike Gears, which had some driving and pushable cover, kill.switch never does anything new. However, it's hard to knock a game that came out 3 years before Gears of War did, so I'll let that slide. Health is also Halo-ish, but it's a bit different. If you take a hit, your health bar will go down and part of it will fade. If the entire bar fades, you're dead. Stay in cover, and the bar will fill in again. You can pick up medkits to refill the entire bar.
Graphics aren't too shabby, but they aren't giving Resident Evil 4 a run for its money. For a PS2, it's all right. The FPS of the game rarely dips, unless there's a lot of physics interaction, like blowing up a glass wall with a cluster of bad guys behind it. During my entire playthrough, I only ran into one glitch, when an enemy from behind a solid concrete wall could see and hit me through the wall. The sound is pretty good, but it doesn't seem like they recorded actual sounds.
The length of the game is extremely short. On the Normal setting, you can expect to play through the game in one sitting, which is about 2 to 2 1/2 hours.
kill.switch is a great game that any shooter fan should pick up. A new copy goes for about 10 to 15 bucks, and a used one goes for 8 bucks to 12. Either way, any PS2 owner should pick this game up.