As E3 began earlier this summer, we knew big things were coming. Announcements like Natal and Halo: Reach, while huge, were the kind of surprises that had just a smidgen of their thunder stolen ahead of time by the rumor mill. But we were completely bowled over when we discovered that THQ and developer Kaos had kept the lid on what looks like one of the next great shooters: Homefront.

Why the fuss? It reminded us of the first time we saw Half-Life — it mirrors that familiar mix of in-game storytelling and ferocious combat. Written by renowned screenwriter John Milius (the guy behind Apocalypse Now and Red Dawn, to name a couple), Homefront flashes forward to the year 2027. After a decade-long energy crisis, the U.S. is in shambles — to the point where North Korea invaded two years ago and now occupies the country. Naturally, you’re part of the American Civil Resistance, trying to beat back the incursion in places ranging from rural Colorado to San Francisco’s Golden Gate Bridge. We love the prospect of a shooter that doesn’t involve aliens or zombies, but rather plausible enemies in very familiar settings — like backyards, malls, and city streets.

On top of that, Homefront is already incredibly good-looking for a game that has no official release date yet (our money’s on late 2010 or early 2011). Part of that appeal comes from some very sharp-looking and realistic settings, like the farmhouse we saw getting shredded in a massive firefight, and part of it comes from how the story-telling happens in-game without cutscenes or camera movements that aren’t controlled by the player. As with Valve’s classic, you’re not running around talking to townsfolk or leveling up; Homefront simply tells its tale as you move around in quieter moments…that are often violently disrupted.

In the sequence we saw, you awake in a safehouse in Montrose, Colorado, surrounded by leafy vegetation in what turns out to be a greenhouse. You’re hurt and you know the occupiers are hot on your trail, pursuing in jeeps. As you gather yourself and walk through the safehouse (which is more like a compound), you talk to the leader as he orders everyone to start packing up and shutting things down. You’ve blown their cover, and he’s a bit grumpy about losing a place that has reliable power and water.

Suddenly, the North Koreans show up, and the battle that begins is brutal in its suddenness and intensity. As the onslaught starts, you’re ordered to move across the street, where you collect a futuristic-looking rocket launcher. Kaos tells us that it’s working with military consultants to include realistic next-gen weaponry, like an adaptive rifle that uses both 5.56 and 5.7 ammo. And something called the Goliath, which we’re admittedly pretty hot for already.

But first, you have to dispatch those jeeps with a few rockets. Kaos is using tech it calls the Drama Engine, which, like Left 4 Dead’s director, brings the action to you. When the player in the demo picked up that rocket launcher, it sent the jeeps over to his position. In other words, Homefront won’t have scripted sequences; the action will develop on the fly, and your path to survival should be different every time.

Back in the battle, the resistance is getting hammered, even with the help of that rocket launcher. You’re instructed to get the Goliath into the action. (Described as an unmanned death jeep, it apparently exists today as an actual real-world prototype!) You use a laser designator to point it at the enemy; the Goliath crashes through an entire house, rolls over enemy vehicles, and unleashes a salvo of rockets that ends the demo with an impressive bang.

Along with this very promising solo campaign, Kaos is also working on a “very substantial” multiplayer complement. Given the terrific 50-player battles it fashioned for Frontlines and the dramatic impact of this demo, we’ll be keeping a close eye on how Homefront turns out.