3. Portal 2
Easily the funniest addition to this list, the Portal franchise is well-renowned for its sense of humour, and Portal 2 makes sure you remember this by leaving you with a hilarious post-credit scene. It involves the quirky robot, Wheatley, floating around in space, apologising for his actions (the player having banished him in space after his spree of insanity). This in itself is comical, yet the creators go a step further by adding another robot who floats in and out of frame, gleefully stating "I'm in space" over and over again as Wheatley continues his short monologue. It's a simple but effective scene, leaving players smiling as they return to the title screen and therefore satisfied (as if the song played over the credits wasn't funny enough).