When Killzone was in development for the PlayStation 2, members of the media were quick to label it the Halo-killer, tough expectations to be sure. Even though the title didn't quite live up to that billing, Sony thought enough of developer Guerilla's futuristic vision to showcase it when they unveiled the PlayStation 3 a couple of E3s ago. We still don't know much about the inevitable sequel for the PS3 but that's okay because Guerilla has been hard at work on another Killzone title, Killzone: Liberation, a third-person action game looking to blow the screen off the PSP.

Liberation picks up two months after the events of Killzone, with most of southern Vekta, the fictional planet, still under control of the sinister Helghast. Under the leadership of General Metrac, the Helghast's next target is the ISA base of Rayhoven, home to a massive cache of ISA weapons. Returning as Captain Templar, players are sent in to hold back the enemy while the ISA VIPs secretly meeting at the facility are evacuated.

Unlike its PlayStation 2 brethren, which was a first-person shooter, Liberation is a third-person action game viewed from a top-down perspective, a surveillance viewpoint that encourages a more tactical approach to gameplay. The battlefields are littered with debris and other means of cover so as players encounter enemies, they can use this cover to their advantage. For example, if you're equipped with a sniper rifle, you can hang back and pick enemies off from long range, whereas if you're holding a shotgun, you'll have to make your way from cover to cover, perhaps while the enemy is reloading, in order to get close enough for the shotgun blast to be an effective means of killing.

The game's targeting system is really well implemented. You hold the right shoulder button to kneel behind cover, then hold the left shoulder button to swivel your weapon and target your enemies. You'll know when you have an enemy targeted because their health meter will appear over their head. Using this system, you won't have to worry about aiming up or down, even if the enemy is on a higher plane. When you're not crouching behind cover, holding down the left shoulder button will allow you to target an enemy and strafe while shooting. It's a very clever way to approach this type of game from a control perspective.

Adding to the tactical gameplay are instances where you'll get to command an AI teammate during firefights and the method for doing so is quite intuitive. To activate the Tactical Command System, you simply press “Up” on the control pad. Different icons will appear all around the battlefield, indicating places where you can tell your teammate to take cover or enemies you can order them to fire at. You can also order your teammate to place an explosive charge while you cover them. The game doesn't screech to a halt when you enter the Tactical Command System, however, it simply slows to a crawl so you can't spend too much time pondering your options. To be honest, I wished there were more times when you could control an AI teammate during the game, the system is that good and the gameplay is that rewarding.

There is also a pair of missions where you'll get the chance to drive a tank and a hovercraft around to help defeat the enemy. Unfortunately these missions weren't as memorable mainly because I found it too difficult to control the vehicles during combat. Both vehicles have two firing mechanisms. For example, the tank has a machinegun turret attached to the base of the vehicle and a tank gun perched atop, which swivels 360 degrees. That means you can fire in two directions at once and you'll have to do exactly that to survive. It's easier said than done. The machinegun will fire directly in front of the tank, which is controlled using the analog stick, while the tank gun rotates by pressing the right and left shoulder buttons. Now take into account that you have to press one of the face buttons to actually fire each weapon, as well as accelerate and reverse the tank, and I'm sure you'll find it just as difficult as I did to do all this in the heat of battle. I quickly abandoned the vehicles in both missions and proceeded on foot, it was simply too taxing to chew gum and drive the tank at the same time.

Putting the vehicle missions aside, the rest of the four chapter, 16-mission campaign of Killzone: Liberation is action-packed as players are challenged to disable an oil refinery, assault a harbor, search a swamp for ISA hostages, and ultimately traverse a mountain valley in order to reach and destroy Metrac's base. The missions are linear, using hotspots to trigger enemy ambushes. Put those two elements together and you'll run into a lot of moments of trial and error in the game. They're not off-putting, however, they'll only make you want to go back and tactically find the correct way to suppress the threat. I did find that level balance was an issue though. I managed to steamroll through the initial chapter but when I got to Chapter 2, Mission 1, I died more times than I did the entire first chapter. There are certain levels that are decidedly tougher than others and there's a boss battle in Chapter 4, Mission 3 that I'm sure will put a callous on the thumbs of even the most experienced gamers.

The singleplayer campaign can be made a little easier if players participate in Challenge Games that are unlocked by completing each of the single player chapters. These games include Target Practice Run, where you have to shoot targets while reaching the exit before time runs out, Base Defend, where you have to prevent Demolition Soldiers from placing C4 at a certain location, and Spidermine Catch, where you have to catch 3 spider mines as quickly as possible. At the end of the Challenge Games, players receive a medal based on their performance and points, which can be used to improve skills and earn new abilities, such as the number of grenades Captain Templar can carry and the amount of damage your weapons inflict.

Liberation features multiplayer functionality in the form of ad-hoc mode. The jewel of multiplayer is the ability to run through the entire single player campaign cooperatively, as long as the host has previously unlocked the missions. If you prefer competition, up to six players can duke it out in one of six multiplayer maps in such modes as Deathmatch, Team Deathmatch, Assault and Capture the Flag. Guerilla has promised infrastructure mode via a patch in the future with two additional multiplayer maps for competitive play. There's also a Gameshare mode where players can share demo levels of the game with other PSP owners.

Killzone: Liberation ranks as one of the best action games on the PSP. The decision to emphasize tactics pays off in spades thanks to an intuitive interface for controlling Captain Templar and the Tactical Command System, where you'll get to occasionally command an AI teammate. The vehicles are a little difficult to control and the levels could be a little less linear, but it's easy to overlook these shortcomings when the rest of the gameplay is as strong as it is. The icing on the cake comes in the form of multiplayer support, both cooperatively and competitively. Whether you're familiar with the Killzone franchise or not, Killzone: Liberation deserves to be in your PSP game collection, especially if you're an action fan.