The co-op mode takes place through the single player campaign with slightly altered content.
The Doom sensation returns with Doom 3! Plunging you right into the depths of Hell, Doom 3 brings to bear its revolutionary new graphics and gameplay engine. In first person shooter mode, you will engage in an epic single-player experience filled with awesome action and a terrifying ambience. You will make your way through grand and claustrophobic levels filled with zombies, demons, and massive monsters. At the end of each tunnel, lurking in shadows, hiding behind doors, are nightmarish enemies that you must blast into oblivion. Clean up Hell! Bam! Boom! Doom!