If the first Killzone was unwisely posited as a Halo-killer, then Killzone 2 was also unwisely said to be the PS3's answer to either Halo 3 or Gears Of War 2. Thankfully, the more time that goes on, the more Killzone 2 has been allowed to stand on its own, judged by its own merits rather than a bullet point comparison versus the exclusives of the 360. This is a nice development, since Killzone 2 is a very different FPS than many are used to and not 1-to-1 comparable.
The game has you as part of a military fleet invading the planet Helghan, home of the Helghast, who did something in the last game, I guess, that warranted such revenge. You don't really need to know, and the game doesn't do much to encourage you to care. Killzone 2's worst element is its plot and characters. It doesn't give you enough backstory or motivation at the beginning, and along the way never builds any sympathy or interesting developments for any of the characters. Everyone seems to fall into stock cliches of the FPS genre, and you could easily replace the cast of this game with almost any other from another FPS and it wouldn't matter. In other words, Killzone 2's Alpha Squad may as well be Gears Of War's Delta.
I don't come to FPS's for their plot and characters, so it worked to the game's favor, in my book, that it attempts so little with them. Instead, the game is borderline daring with its gameplay, and specifically, its controls. Coming to Killzone 2 from other games, your first impression will likely be that it's sluggish and unresponsive. Even with the sensitivity jacked up all the way, your aiming reticule moves about as slowly as Call Of Duty's set to its lowest speed. At the same time, your character's movement, even when sprinting, seems slow and awkward. However, the more Killzone 2 I played, the more I began to embrace this difference. The game is aiming for a very deliberate pace, as well as a sense of heft, weight, and visceral-ness that is missing from most titles. You aren't as nimble as even the thick necked Gears Of War dudes, but Killzone 2 feels all the more distinctive because of it.
I had to stop myself from typing "realistic" in that last sentence, but maybe that is a better way of describing it. If the Halo series has a weapon design philosophy that screams "I grew up with Nerf guns and don't care how absurd things are as long as they're fun", then the Killzone 2 team likely grew up watching History Channel documentaries on the guns of World War II. All of the weapons in this game feel heavy and (for lack of a better term) realistic. The sheer sound design and reloading mechanisms of the guns are excellent and tell you more about the two opposing sides than any of the story. Your side's assault rifle has a laser dot scope and a sports-car like finesse to it; the Helghast assault rifle--which I used for 90% of the game--is raw and LOUD, with old school iron sights and all. Better still are the parts where you get on turrets or vehicles. Rather than having the usual "weapon heat" gauge pop up on screen, you can tell the turret is overheating because the gun barrels begin to glow red hot. Furthermoer, the 'robot suit' section doesn't have health or heat meters; you know you're getting messed up because the thing starts emitting alarm noises and the glass on the cockpit cracks. It makes the game more immersive, though I could have done without the parts that use the Six Axis motion controls to turn wheels and plant bombs. They work fine but do feel unnecessary when a simple button press would suffice.
Killzone 2 is a great looking game even if it's nowhere near as stunning as it was back when it was first being shown. On top of everything looking good, it has a real sense of "place" and setting due to its well thought-out aesthetics. Helghast troops vary in their uniforms and amount of armor depending on what their primary weapon is; those with SMGs have very little and will whip out a knife at close quarters, while those with flamethrowers take a hefty amount of shots to put down since, realistically (there's that word again), you would want as much armor as possible between you and a ruptured fuel tank. All of that said, the level design of Killzone 2 is your bog standard FPS stuff, with endless house to house urban combat, industrial warehouse crawls with vertical mazes of catwalks, and even an assault on a palace, complete with a section where you have to fight waves of enemies to get a boss to fight you himself.
Speaking of the bosses, the difficulty of Killzone 2 seems to vary wildly depending on what your current objective is. If it's just making your way through areas, it can be fairly easy to slightly challenging. If you're trying to do something specific, like, again, fight a boss or out-shoot some snipers, it becomes frustrating and unfair. There's a boss fight early on against a flying robot that nearly made me quit the game, since having to rapidly hit certain things, switch to a different weapon, and shoot the boss throws into stark contrast how deliberate and unresponsive the controls are in a situation where you need both accuracy and speed. It doesn't help that, while you can revive your downed teammates, they can't do the same for you. Moreover, Killzone 2 suffers from the usual modern day, Call Of Duty-design philosophy of "difficulty" meaning the following: all of the enemies have preternaturally good aim at distances they shouldn't with the weapons they have; all of the enemies seemingly focus entirely on you; if you get shot more than a few times you have to desperately backtrack and hide until your health repairs itself. This last bit is especially troublesome during the boss fights, because they can kill you very easily while you have to unload on them again and again, all while balancing this with trying to stay in cover without getting shot so your health can restore itself.
Yet despite these problems, I came away from my experience having some newfound appreciation for the FPS genre. Killzone 2 has its flaws, and isn't the most original or deep game, storywise, but the ways it is different from other FPS's make it a standout title that I think everyone should try. Maybe even after a couple hours you will hate the way it controls and feels, but its deliberate pacing, sense of thickness, excellent graphics and weapon design, and "realistically" visceral combat are unlike any other FPS I've played.
(For the record, I didn't try any of the mutiplayer, but it's not like that would ever detract from my scoring of a game)