Is dot Hack actually good?

I've been avoiuding Dot Hack in all it's forms.  Is it worth it to play through all four games, or just avoid it?

Actually, one thing really bothered me about .Hack

I've only played the first game, and I noticed that on your mailing screen, it sorta comes up like a browser, and where the web banner should be on the top of the page, there is a graphic you can see but it's in poor quality.

I studied it for a little bit and found out it was a graphic of the cat girls from "Tail Concerto", which if I remember correctly, Bandai had NO FUCKING COPYRIGHT for!
How the hell did they get away with this?