Here is an overview of the Year One Pass, via its Steam page:
The Slayer’s legend grows…
Your victory over Hell’s armies pulled humanity back from the edge of extinction, but it came at a cost. An imbalance of power in the heavens requires the true ruler of this universe to rise and set things right. Wage war across never-before-seen realms of the DOOM Universe, fight against new demons, and wield new abilities in your never-ending battle against the forces of evil.
View the screenshots at the gallery.