I think that you should just play the ones you like. If you don't like a game, or if it doesn't seem good to you, skip it. You don't really get anything out of playing a game you don't like, do you?

And I don't see how playing each one in order makes the games better. I mean you can see how technology has advanced through each one, but that's about it. The storytelling really varies from game to game, so you really can't say XIII is better than X is better than V, just because XIII is the newest. My personal favorites are VI and VII. Is XIII better than both of them just because it's newest?