You will think you get it, but you really don't.
For example, I bet that people who haven't watched the anime still have no idea who Shino is, and why Haseo seems to be attached to her so much, or why Ovan keeps appearing and stuff like that. Another one would be Phyllo's short appearance in ep.2, even though you would know he's dead in RL (cancer if I remember correctly)if you actually watched the anime, so it wasn't possible that he was the one sending you those emails.
Also from what i've seen/read, many many characters from the anime series make their first appearance in the game in the 3rd installment, so I would suggest watching the anime series before the game comes out regardless of whether you think you understand the story or not.
And i'm not even interested in animes really, not even remotely... but I did watch the .hack so I could understand the G.U. storyline a lot better (I played through the entire 1st episode without the anime, then went back and replayed the first game after finishing watching the entire anime series and I picked up a lot of stuff that I would otherwise not get if I had not watched the anime... that's the way Bamco does things I guess. Mistwalker is currently doing the same thing with Blue Dragon.