I disagree. Marathon is all right but compared to Doom, Marathon's movement is awkward, its level designs a convoluted jumble, and its graphical textures murky -- chalk it up to ambiance if you want, but I think it was more inexperience on Bungie's part and the insufficient hardware of the time.
I found Durandal to be a much better game and still play it every few months on my Xbox 360.
Very much agreed.
None of the above (whether one agrees or not) really refutes the initial point, which is more about the content. Doom's premise is, to be charitable, threadbare, the thinnest possible excuse for putting the player in an environment they say is a base on Mars and fighting against demons from hell. There really isn't any more to it than that, and the mixture of environment designs is schizophrenic to say the least, a trend that would continue in iD's next hit, Quake.
Marathon creates a detailed and believable world, with art direction working harmoniously with the text of the story told through the game's AI terminals. Effort was put into making the maps functional and believable in many cases, and Marathon's world is not, generally speaking, strewn with burning, explosive barrels for no reason other than that they blow up real good.
Level designs a convoluted jumble? One might well say that they took advantage of the pseudo 3D of the time to make legitimate labyrinths that required a deliberate effort to explore, something that rarely is the case in today's high definition shooters, and something I miss.
Murky textures? I don't think we're talking about the same game. Textures onboard the colony ship Marathon are shiny and high-tech; it's actually Doom that's muddy a lot of the time, with everything moving towards a muddy red-brown as the game progresses and the player ventures further and further into Hell. Often, Doom levels appeared to be entirely abstract, and the idea of being on an extraplanetary base or on the surface of another world was more a mild suggestion.
No disagreement that Marathon 2 is in many ways a superior game, but I felt at the time and feel now that in many ways that are important, Marathon was a competent and fully-realized story-based shooter in ways that Doom in all its incarnations, new and old, never really was. In many ways Marathon is better than its stepchild, Halo.