The first series is 4 games long.

This new series is 3 games long.

Should you buy them? They are not for everyone...no question about that. To get the full story you would need to watch .hack//Sign and play the four original .hack games. In addition to the games there is a 30-45 minute OVA...OAV...whatever! that comes with each game.

Also the history of the events before anything can be important. It is a series that requires a lot of interest. Check out Wikipedia.

http://dothack.wikia.com/wiki/.hack//Wiki

Check out www.gamerankings.com for a multitude of reviews for all the games.