Metro 2033 Redux

Metro 2033 Redux is a first-person shooter from 4A Games based on the novel by Dmitry Glukhovsky. After a nuclear war, survivors hide in the Moscow metro, where station-states fight one another and mutants roam the surface. Redux is the remastered version with improved visuals.

It plays as a mix of stealth, shooting and survival. Ammo is scarce, military-grade rounds double as currency, and on the surface you have to change gas mask filters in time. The flashlight, watch and mask are part of the interface, which adds to the sense of presence. Before each encounter you decide whether to sneak past or fight.

The story takes about 9 hours, and a 100% run about 24 hours (according to HowLongToBeat), so a month at 2 hours a day is plenty. Single-player, no online connection needed.