If the latest Marathon reveal by Bungie isn't your jam and you want a more classic experience, you might be interested in the sequels to the Marathon trilogy already available to play.
The Marathon IP was the one that put the acclaimed creators of Halo and Destiny on the map. Comprising three games: the original Marathon, Marathon 2: Durandal, and Marathon Infinity, the franchise developed a cult following in the years that followed. This led to two fan-made projects that continue the story of the original: Marathon Eternal and Rubicon.
Bungie is known for actively supporting community efforts and giving players the tools to create their own unique scenarios. The company open-sourced the original Marathon 2, which eventually led to the creation of the Aleph One engine. This engine can now run all the original Marathon trilogy, as well as third-party "scenarios," such as projects like Eternal and Rubicon.
Essentially having Bungie's blessing, both Eternal and Rubicon expand on the massive lore the original trilogy set up. They aren't projects that complement each other, though. Think of them as alternate scenarios where events occur after Marathon Infinity.
Eternal, for instance, takes place 94 years after Infinity. It's unclear whether your original efforts were worth it, as the Earth is completely decimated. So, naturally, the only course of action is to travel back in time as you try to bring a true, solid victory to mankind. At least, that's what you think you're doing at first.
Rubicon is just as ambitious, if not more. Taking place 50 years after the original trilogy and following the events of Marathon 2's ending. The game features branching paths based on choices you make at the end of certain scenarios called planks.
Both games are rather fascinating. Perhaps the gameplay might not be right up your alley, but the storytelling is very much in line with Bungie's, and even if they are technically non-canonical fan-made projects, if you found yourself completely immersed in Marathon's original trilogy plot, then these are worth your time.
Hopefully, Bungie will be able to rekindle that sense of mystery the original game had. In any case, Marathon (the new version) is releasing on September 23 for PC, Xbox Series, and PS5. You won't need a PSN account to play across multiple platforms. And as a reminder, if you're in North America, you can sign up for the Closed Alpha testing.