I would recommend you to read A Theory of Fun for Game Design, written by Raph Koster, an experienced game designer who started as a writer.
He basically proposes that we humans are living things that love watching and learning patterns everywhere. We basically want to get better at things, and games are a powerful learning tool. Games offer simple mechanisms that add themselves up to enable players to do really complex stuff (e.g. see how a player who loves playing fighting games learns to play those games).
What makes a player to return to a game? A fun mechanism is vital, but there is also another ingredient. Remember when you learned how to play Tic-tac-toe? it was a pretty fun game until you understood how to play it, and what strategies you used to win or tie every time. When we begin doing any activity (being playing a game, playing an instrument, painting, etc.) we start to do exactly that: learn what are the best strategies to do best what we like to do. If the activity is simple enough to know those strategies quickly, then that activity becomes boring. If the activity is too complex, we also get bored and we opt out of it.
So there are two extremes, see? assuming that we like what we are doing, if it's very simple, we will get bored quickly because our brain concludes that it took everything he needed and can predict now the next steps. If it's very complex, we will also get bored because we are unable to grasp the concepts that enables us to win the game/paint nicely/play clarinet beautifully.
So games are especialized in that: they present an activity with a carefully balanced difficulty setting, so the game is easy on us when we learn the controls, but as we gain experience playing it, the difficulty keeps rising and rising.
When we get to this fragile state of mind, we call that being "in the zone". That's an important thing to achieve when designing a game, and watch people who play if they're in the zone, whether they're playing WoW or minesweeper.
You should also read the Princess Rescuing Application slides, by Daniel Cook, which also present an insight on how games trap us.