Before Halo, and before [Bungie shoved microtransaction cucked nigger dicks up our assholes], there was a game that was ahead of its time, versatile, and perhaps even deeper than anyone could have imagined (at the time). You play as a space marine, dubbed MJOLNIR Recon #54 is set on a mission to a UESC military installment on Deimos, the asteroid moon orbiting Mars, after a suspicious drop in communications. It is currently administered by three AI's, Durandal, Leela, and Tycho. Two out of the three AI's, Durandal and Tycho, have been compromised with the former going rampant and the latter being corrupted by the oppressive alien invaders known as Pfhor who seem to have enslaved an advanced race originating from the war-torn planet L'Howon. Leela attempts to bring some semblance of order to the Marathon, but is ultimately lost in the conflict.
SCENARIOS
Marathon is a versatile game with Forge & Anvil and other scripting tools, some of the greatest scenarios are listed here.
But there are two scenarios in particular that are really a good service to the fans and are definitely friendly to the lore and bring the story down to earth for those who are having bloodshot eyes after reading every single terminal in the official trilogy.
Here we have the unofficial fourth chapter in the Marathon series, with two separate plot lines following Infinity and its bizarre use of deep themes to determine where you go after a certain objective is complete, so you can end any greater mission on a happier note or a bitter note if you wanted to. Failed timelines are actually possible in this scenario, like in Infinity.
This is probably the most epic scenario I have ever played, the levels are absolutely fucking GINORMOUS for a good majority of them being based on familiar/popular ones in the official trilogy. I won't spoil it too much but like Rubicon before, there is a huge amount of variety in not only level design and story paths but the amount of careful decision making in such a classic format shooter is nothing short of impressive.
Here's some badass music.