A first- or third-person shooter with both an epic single-player campaign and perfectly tuned, well-thought-out online play has become the white whale of video game design for the PlayStation 3 and Xbox 360. Both consoles are home to wonderful, single-player adventures and endlessly fun, battle-tested multiplayer bloodbaths. Yet no single game has hit the sweet spot, combining a compelling narrative and convincing acting with online gameplay that keeps the title fresh months after you’ve finished the offline part.

“Killzone 2” (rated M, $60 on PS3) falls firmly in the “decent online, so-so offline” camp, but not before teasing with a fantastic intro movie that only sets the stage for disappointment. An all-too-familiar gantlet of challenges has you checking out a downed aircraft for signs of survivors just in time to see the last one die, battling to gain control of a bridge, fighting your way to the front of a moving train, shoot down enemy aircraft with a turret, evacuating a disintegrating space ship and other missions you’ve probably finished half a dozen times in other, similar games.

The plot of “Killzone 2” revolves around invading the planet Helghan, the homeworld of an offshoot of humanity called the Helghast. In the first “Killzone” on PS2, the Helghast staged a surprise assault on a planet controlled by the Interplanetary Strategic Alliance. In the sequel, you play as Sgt. Tomas “Sev” Sevchenko, an member of an ISA special forces unit tasked with infiltrating the Helghan capital and capturing the planet’s dictator, Scolar Visari.

Like a lot of video game sequels, “Killzone 2” could use some kind of “previously in ‘Killzone’ and ‘Killzone: Liberation'” movie to set the stage. Those of us who didn’t play “Killzone” or its PSP sequel would probably be more fired up to stick it to the Helghast if we were brought up to speed on their previous assault on the ISA planet of Vekta. But even the most basic information on the world and characters of “Killzone” is missing from the game’s instruction manual. I had to turn to Wikipedia for all my exposition. I realize first-person shooters are the video game equivalent of summer blockbusters; few people play them for the story. But a little exposition would go a long way.

That’s not to say the the opening moments of “Killzone 2” aren’t memorable. The game begins with a defiant speech by Visari, brilliantly brought to life by veteran Scottish actor Brian Cox, as ISA forces begin their D-Day-like assault on Helghan’s heavily fortified defenses. The heart-pounding score, fiery oratory and “Saving Private Ryan”-style shots of the battleground hoodwink you into thinking you’re in for a series of white-knuckle battles tied together by a decent war story.

Sadly, Cox (a Shakespearean actor whose voice you may recognize from his turn as a screenwriting teacher in Spike Jonze’s “Adaptation”) is absent for the majority of the rest of the game. Most of the rest of the actors, as well as the lines they’re given, never approach the quality of that first tease, and much of the dialogue is unprintable on the website of a family newspaper. The overall effect is as if Ben Kingsley were cast in an episode of “Rock of Love.” Cox sticks out like a sore thumb.

Ham-handed writing aside, the production values are as good as anything you’ll find in console gaming. The toxic, barren world of Helghan is rendered stunningly via its bomb-cratered urban wasteland, Nazi-inspired architecture and air so choked with toxins it makes Beijing look like Antarctica. (For some unexplained reason, the Helghast wear gas masks on their inhospitable home world, while the maskless ISA troops never so much as cough while fighting through the haze.)

While pretty much all the levels of the single-player game will remind you of something you played somewhere else, they all look fantastic. Designwise, most levels have you using the game’s cover mechanic to slowly inch forward, capturing one key choke point at a time. The Helghast are a fairly cunning computer-controlled foe, as well. They seem to realize the importance of holding choke points on the map and will sometimes force you to temporarily back up. They also do a fair job of flanking you. On a few occasions, I was convinced I’d covered my behind, only to have one or two Helgast slip behind me and start blasting away. You can never get too comfortable.

Ultimately, though, the familiar gameplay, weak writing and generally short campaign mean folks only interested in offline play will want to make “Killzone 2” a rental or budget purchase. Online play, however, is well-tuned and robust.

For those looking for PS3 online experiences similar to what you’ll get on the Xbox 360’s “Halo 3” or “Gears of War 2,” “Killzone 2” should be your first stop. Though it doesn’t support as many features as those titles, it does offer a “Call of Duty”-style hierarchy with several classes of specialization to choose from. The game also features a clan system that lets you unite with other, like-minded, similarly skilled folks.

“Killzone 2” ships with eight, well-balanced (if sometimes overly symmetrical) multiplayer maps and a variety of somewhat standard game modes. (Two pieces of downloadable content priced at $6 add two new maps each.) My favorite game type was Assassination, in which one team is tasked with taking out a specific player on the other team. The target must stay within a designated area, and his teammates must do everything they can to keep him alive until the timer runs out.

Other game types include capture-the-flag variant Search and Retrive, team killcount varient Body Count and a territory-control mode called Capture and Hold. A fifth game type, Search and Destroy has one team trying to set explosive charges to destroy a target, while the other team defends.

Between the eight to 12 maps, five gametypes and deep class system, you’re unlikely to run out of things to do online. If throwing yourself into the fire against a bunch of l33t strangers isn’t your bag, the skirmish mode lets you practice the online modes offline against computer-controlled bots. The only things really missing are a couple more game types and online co-op play during the campaign. The latter, in particular, seems like it should be a given when Sev’s got at least one guy fighting alongside him for much of the game.