Love .hack One of my favorite anime series'. I haven't seen any of .hack//roots yet though :(
As for the games, they're a necessary part of the series. You really should play them all the way through. I found them very fun. At the very least, you should read "Another Birth". They take place during the game and give you a basic idea of what happens in the games. All three of them are out now (at least in the US).