Why do we feel the need to buy new games?

[The_Liquid_Laser]

Most good games have a high replay value.  If you like playing that game, then play it again.

There is a concept in economics called diminishing marginal utility.  If you consume something an extra time, you don't get the same amount of enjoyment out of it.  The second slice of pizza is not as tasty as the first slice, even though the two slices are identical.

Many games work this way, especially if it is a story/adventure type game.  After you've experienced the story or adventure once, then it won't be as fun the second time.  On the other hand, skill based games have a higher replay value, because the fun is in building your skills rather than going through a story.  If you play Smash Bros, then it can keep being fun each time if you feel yourself getting better at the game.  Plenty of games have a mix of these two elements.  You might enjoy the story or adventure once, and that aspect becomes less enjoyable, but at the same time if you are building your skills, then the game has you hooked and you want to keep playing.