I'm actually a big fan of the series, though the anime is merely 26 episodes and does wrap up that arc with its characters, it spans a very large collection of media to tell its full story. To give you an idea of what this anime started:
- .hack//Sign
- .hack//Liminality [OVAs] which run along side the story events of the four games of .hack//infection, .hack//mutation, .hack//outbreak, and .hack//quarantine
- .hack//Legend of Twilight (Tasogare no Udewa Densetsu)
- .hack//Gift [OVA]
- .hack//Roots
- the four .hack//G.U. games: Rebirth, Reminisce, Redemption and Reconnection.
- .hack//G.U. Trilogy [Movie] (this kind of sums of the three main games in a slightly different yet more epic way)
- .hack//G.U. Returner [OVA]
- .hack//Quantum [OVA]
- .hack//Sekai no Mukou ni [Movie]
- .hack//Link
The above is just the media, there is a ton of books to go along with it as well.
Getting back to the subject, .hack//sign though does have some decent action scenes, you should be aware it is a lot of talking but in very interesting and philosophical ways. If you're the type of person to listen, you can get into a pretty deep story with this series that keeps me giddy to this day.