As a former hard core gamer, I had high expectations of this series which has been languishing in my list of stuff to someday get to watching. So I started viewing this intending to finish all the .hack series.
Story/Character
The premise is exciting - one player in "The World" is suddenly unable to log out - why? The mystery gets deeper and deeper as we are pulled into his life and the life of the other characters (in game and in the real world) who either want to help him, want to solve the mystery or have some other hidden agendas of their own.
The set up (first 8 episodes) was very well done. Just as I started to get fascinated the series went on a philosophical bent and the plot stagnated. By the time it tried to recover I was frankly pretty bored and was just going through the motions of finishing the series.
The characters are a mish mash. Some you remember and some could actually have been left out of the anime without making any impact at all. It was hard to even like any of them except 1-2 (you'll know what I mean).
Art/Animation and sound
The animation was great for that time. Very cute and I can see where "World of Warcraft" may have copied some of the stuff. Songs were pretty decent but not as good as the art. It's a very pretty anime and as a gamer I was satisfied with both.
Enjoyment
The series starts well, gets slow in the middle and tries to end with a bang but somewhat fails to pull it together. The end is ambiguous which detracts from overall enjoyment, hence the low score.
Overall
This is one of those polarizing anime. You either love it or you hate it. There are a lot of similarities to "Serial Experiments Lain" (which I hated) but I scored this a lot higher due to the effort it took to make the gaming world realistic, which I really appreciated. Overall I gave this a 5 -- there was much more that this series could have done that they didn't do, and the slow pace really made this less enjoyable than I would have liked.