And being able to carry a good chunk of weaponry.
But yeah, until there's a lot of information put out, the Doom Marine is much more human than the Space Marines.
If anything, he's augmented by soul spheres/ Beserk packs/invulnerability artifacts/etc/etc.
Maybe they give him the ability to carry a lot? Well, on a Beserk pack, he can punch out a Cyberdemon in less time than it takes to kill it with rockets.
I don't know. The thing is, if you really want to bring in Augmented humans, I nominate Aya Brea from Parasite Eve. Because as awesome as Samus is, she can't create nuclear (Fusion, not fission) explosions with the power of her mind, get completely engulfed in said explosion, and not end up with a single scratch.
Plus, Aya can lift up a 18 ton (More or less) railgun mounted on a Satellite.
I like to see anyone else do that, including the Doom Marine.
So, I would have to say, the Doom Marine is one of the most powerful video game men. "Rip and tear!"
But Aya trumps him and Samus, and the Space Marines. And yes, even Superman, due to his psychic weakness.
Also, unlike all previous characters mentioned, besides Superman, she can't really die, unless it's in a player controlled way. Such as being hit by too many enemies at once.
So, yeah, immunity to all forms of being killed, or just about.