Portal 2 (2011)

The separate two-player campaign is organised into courses and short test chambers, with a genuine conclusion beyond the last puzzle. Roughly 5–8 hours is a sensible starting budget, depending on how long the pair spends reasoning. Completed chambers provide natural session boundaries and replay selection. Two people are essential, but the game tracks cooperative progress rather than demanding an uninterrupted run. A substitute can join, although returning to missed chambers is the fair way to keep both partners involved in the discoveries.