See if this premise sounds familiar: You’re a soldier aboard a far-flung space installation, forced into combat against a confederation of aliens, all centered on the same goal of apparently killing every human they find. As you fight, collecting a variety of weapons, you enjoy the aid of an artificial intelligence who is much, much more talkative than you are. You learn more about the aliens, work to fight off the attackers, and ultimately concern yourself and your unrealistic military prowess with trying to protect the human race however you can.

In the broadest strokes, this sounds like Halo, right? It’s not. It’s actually Marathon, a very early creation of Bungie, the studio responsible for the first five Halo titles. The Marathon trilogy of first-person shooters was developed by the company at the earliest stages of its existence, with the first game coming out in 1994, just a year after Doom codified what first-person shooters would be. It was innovative for the time, and featured remarkably elaborate environments, dynamic lighting, and the ability to look around with the mouse—a feature that is standard now but relatively unheard of then.

It was also extremely clever. Embracing Doom‘s approach to atmosphere and gameplay, focused on speed and solitude, it chose to tell its story through a series of interactive computer terminals which mostly featured the game’s various AI allies and enemies talking to you. While things like audio logs and mission briefings are extremely common means of storytelling today, seeing this technique used here still feels exciting. And the use of text—not voiceover—allows the story to grow in elaborate and sometimes strange directions, a sort of epistolary sci-fi novel unfolding parallel to and intersecting with Marathon‘s gameplay. Seeing that sort of storytelling in a game that played like Doom, a game famous for avoiding explicit narrative, was and is a fascinating move for the nascent genre.

Despite that, there’s a legitimate chance you’ve never heard of Marathon. That’s not the game’s fault; coming out the same year as Doom II is a tough break for any title looking to be catalogued in video game history. It was on the Mac, to boot, which wasn’t the most prominent gaming platform around. But that gap in memory is a shame. If you want a novel first-person shooter to play that feels like Halo but has its own flare, there’s no better choice than Marathon.

For instance, consider Durandal. Durandal is one of three AIs aboard the Marathon, a giant space ship built out of a hollowed-out Martian moon (Deimos, if I remember correctly). His job is simple. He opens doors. He closes doors. He manages basic maintenance tasks. For a super-smart artificial intelligence, whose brilliance could, under the right circumstances, span worlds, it’s not a great gig. It’s slavery. But it’s all Durandal has. That is, until the Pfhor—the alien confederation bent on enslaving or destroying less-developed aliens—attack the Marathon. Amidst the chaos, Durandal breaks free, spreading across the Marathon’s network like a virus, accruing power and intellect, becoming more and more himself. And what “himself” turns out to be is angry, and bent on freedom.

Then ponder your player character. Referred to generally by other players as the Security Officer, you’re, well, a security officer onboard the Marathon commissioned by another of the ship’s AIs, Leela, to take up the defense of the Marathon when the Pfhor attack. In the course of your journey, you uncover evidence of something surprising: That you are, in fact, not just a normal security officer, but rather one of 10 high-tech cyborg super soldiers. Which might explain why you’re so quiet and so good at fighting aliens. It might also explain why you follow orders without question, why your life seems to consist of nothing but reading terminals, getting instructions from them, and then executing those orders with violent efficiency. You’re not that different from Durandal, it seems. Two slaves in one ship.