I've recently watched the first two OVAs of .hack//Quantum, and I have to say it's renewed my interest in the franchise. .hack// has always been a favourite of mine; I simply love the universe it's set in. While the stories tend to be fairly similar (people being trapped in the games, unable to log out or put in to comas) it's always interesting.
I haven't actually watched many of the anime, but I read .hack//Legend of the Twilight Bracelet and a few others, and watched .hack//G.U (as well as read a few volumes of the that particular series (recently finding out that even though it seemed to end there are more volumes available) as well as having played the original .hack//Infection (although never really getting far in the series - something I hope to fix over the summer).
Anyway, I love this franchise <3