You're in an aircraft, clouds rushing by. As it banks, you see a massive fleet of other craft like yours dotting the sky. You're manning a door-mounted gun and, until an Ork with a jetpack floats past, you could easily be in a Modern Warfare game.

“This is a fresh take on Warhammer 40K,” says game director Raph van Lierop. “We've been looking for a way to explore aspects of it that don't make sense in an RTS, [and] here we have an opportunity to bring it to a much broader audience. It's about understanding what aspects to express to players that aren't familiar with the IP. Once they get in there, they're like, 'Oh shit, I didn't realise this was so fucking cool and there was so much depth here and so much I can do!'”

Space Marine is a thirdperson shooter set on a Forge World, an industrial planet that produces mountainous death machines called Titans. It's been overrun by a million Orks, and – a sentence I write way too often in this job – your dropship has crash-landed, leaving you alone behind enemy lines.

Action games aren't ordinarily Relic's thing. Console-only World War II shooter The Outfit was their experimental first step in that direction, and while it mixed strategic elements in effectively, criticisms centred around the flatness of its combat. They don't seem the most obvious choice to turn the Warhammer 40K universe into a twitch carnage game.

They're not oblivious to that. In fact, their first move was to poach around 50 new hires from rivals and successful action studios, including people who've worked on Counter-Strike and Half-Life. Raph says: “We knew that we wouldn't be able to be competitive without bringing in new talent... We have almost 100 people on the team; I'd say probably half are new since the beginning of the project.”

If you read any other previews of Space Marine, you'll probably find a Gears of War comparison in the first or second paragraph. I ask Raph if they're sick of it yet, and he says just the opposite: Gears of War is the gold standard of the genre they're just starting out in. “When you're comparing favourably to the best games in the world,” he explains, “you're probably doing something right.”

So it's over-the-shoulder shooting, hordes of enemies, and occasional squadmates to exchange manly exposition with. If anything, the Gears of War comparisons might be overcomplicating it a bit; that game is about using cover strategically, while Space Marine doesn't concern itself with such trivialities. There's cover, but a space marine has no 'hide' button. Rather than when to shoot, it's a game about who to shoot first.

The main reason to care about Space Marine, really, is that it's 40K. It's an amazing universe, and one we rarely get to see close up. The first time you see an Ork Nob – armoured close-combat warriors – bear down on you from this perspective is the first time you realise just how big, spiky and terrifying they actually are. Despite the silly name.

The best part of seeing Warhammer fleshed out this way is the Plasma Gun. In Space Marine, you start with a bolter and chainsword, which you can purchase upgrades for once you've killed enough stuff. But you can also find entirely new weapons, and the plasma gun is the star so far. It has a muscular punch to every shot, and when it doesn't rip an Ork's arm, head or legs off, it obliterates them in a light drizzle of blood. If the game is good, it'll be because of weapons like this.

Guns are only part of the focus of combat: with this many Orks in combat spaces this tight, your chainsword sees a lot of use. A basic attack is enough to splat the average Ork, but you can also use 'sync kills' to finish off tougher enemies, hurling them to the floor and stamping on their face, or lifting them up and shooting them. There's a bull-rush move if you're particularly eager to get to melee range, and the popular but seismologically dubious stomp move to stun enemies.

I saw three sections of Space Marine, each of which involved shooting and slashing Ork after Ork after Ork. In case it's not clear, you kill Orks in this game. If you do anything else, ever, Relic aren't talking about it yet. They won't even say if the variety stretches as far as killing non- Orks – when I ask specifically if there are other types of enemies, Raph will only say, “There's a lot more going on on this planet than just Orks invading.”

Is that enough? If the killing's good enough, of course it is. Does it seem good enough yet? Occasionally. Space Marine feels like half an idea for a game: I kept waiting for Relic to tell me the twist, the innovation, the experiment. Some games don't have one, and that's fine. Gears of War is fine. Gears of Warhammer would be fine too: I'd play it. But from the creators of Homeworld and Dawn of War, I can't help wondering if they have something else up their sleeve. And if not, why they're the ones making this.