5. Portal (4 hours)

Portal’s campaign did not last that long, but this is still one of the most original games made to date.

This 2007 game obviously did not have the longest single player campaign made to date, but delivered some of the most original gameplay yet seen in a video game. Focusing on portals, the game let players open portals on a level’s surfaces like walls and floors, with a pair of portals being connected, allowing players to enter one portal and exit through another.

This great gameplay mechanic was used to get through the game’s different levels (known as test chambers), and plenty of lateral thinking was required to get through the most difficult chambers. The game also featured one of the most memorable video game characters ever, with the artificial intelligence known as GlaDOS delivering most of the game’s witty script, which had no shortage of funny lines. So even if this is not the longest game around it is still a bona fide classic worth playing (or replaying) again…