The .Hack games never really impressed me. I mean I like the idea behind them, and the basic story but the execution left much to be desired.
My biggest problem with the first game series was that each of the games felt like one forth of a game rather when a whole game by itself. I hated having to pay full price for four titles that together made one full game.
I have not played G.U. so maybe it does not have the game problem but after the first series I had no interest in giving it a shot.
I'm also not really a fan of MMO RPGs or Single player RPGs that mimic MMOs like this games case.