droid said:
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It depends on the situation. If they haven't played games for 15 years thats very different from not at all.
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I agree, it definitely depends on the person and what you're trying to accomplish.
If you're trying to convince your crazy aunt that games aren't all about guns, violence, and gore, a game like Portal would be fantastic.
Or, if you need to show that games can be a deep and moving medium for story and character development, Portal still works for that, too; but others like Shadow of the Colossus, Mass Effect, or Final Fantasy X (imo) are good as well.
When you want to show that games can be a form of art, Okami or Psychonauts might be a good selection.
If there are those who complain that games are just mindless button-mashing and slack-jawed entertainment, any puzzle game will do really, but Valkyria Chronicles, Tetris, Legend of Zelda (any), or Portal (again) could be good examples.
If all you want to do is show how much fun they can be, simple games like Portal (again!), Plants Vs. Zombies and Katamari Damacy are great ways to go.
I find it difficult to represent the game industry in a single game; it's too big and complex for that (that's a good thing). It's better to display the different facets it has and lead those curious to one that they enjoy the most.