I've read contrasting reveiws about .hack//sign. What I personally think is that I could very well have avoided wasting my time watching it. I don't know, maybe there is a good story somewhere along the way and I missed it because I was sleeping - but really, even if that is the case, then you must agree with me that the execution is terrible. The reasons I'm rating it so low are: the pacing is painstakingly slow; there is very little character development; the backstory is only hinted at; there are several issues (even main ones) and sub-plots that are left without a conclusion. It only gets interesting towards the end, so it could have been developed perfectly well in 12 episodes instead of forcing the viewers to watch all those epidoses where basically nothing happens and the characters are only discussing what they should or could do and summarising the very little information they have - I honestly found all these conversations extremely boring and stupid.
The idea behind it is probably original if .hack//sign is the first anime to narrate the story of someone trapped in an online game. Tsukasa, the protagonist, is in fact unable to log out from this game which is set in a virtual reality called "The World". He also seems to be suffering from amnesia and to have weird powers and this sparks the interest and curiosity of some other players; some of them feel for Tsukasa and are worried about him, while others are intrigued by the fact that there is a player who is not subject to the general rules of the game, an anomaly. So the plot revolves around Tsukasa (reluctant at first) and this group of players trying to understand what's going on and solve the mystery. The plot could be interesting, but as already said the execution is bad; apart from the pacing, at the end we do get an explanation of sorts but too many things are left unresolved and unexplained: who is the mysterious entity that trapped Tsukasa? why doesn't she want Aura to awaken? what exactly is Aura's role in the game supposed to be? why was Tsukasa chosen? what happens to Sora? and what about Macha the cat?...and so on and so forth. So to summarise: plot holes, unresolved issues, unexplained backstory, slow pacing and dialogues so nonsensical they made me want to cry.
As for the characters, Tsukasa is extremely unlikeable for 2/3 of the anime. You don't get why the other characters care for him nor why should the veiwer. Towards the end he starts getting more likeable and as he changes I guess you could say he also develops. But I'd say that when you start off with a character who can only say "Leave me alone" and "You're so selfish" it doesn't take a lot to make him undergo some development just by showing him open up a bit more to other people. As for the rest, no development. They just have a few quirks to make them distinguishable from one another and the backstory of some of them at a certain point is revealed.
The animation and visuals in my opinion are quite bad. The music is good and varied, but several times it sounded a bit off to me, as if there was no connection between the soundtrack and what was going on in the anime.
Overall, I wasn't impressed at all by this anime. To me, it was a waste of time. But, as I said at the beginning, there are many who don't agree with me and consider .hack//sign a good anime. So watch it and decide for yourself :-)