Incredible...
Gameplay, in general, is tons more interesting than the original .hack series was. For starters, you now gain spells through items, and attack skills through your weapon skill level (independant of the weapon you are using, but dependant on the weapon *type* you are using; for example, your Twin Blade and Broadsword skill levels increase independantly). You get the ability to wield either Twin Blades, which are quick but weaker, or a Broadsword, which is a massive two-hander (think Cloud from FFXII) that is good for massive hits that can stun or knock your enemies up into the air. The Scythe is not included as a usable weapon in Vol. 1. There is also another aspect of battle, called Avatar battle, that is interesting, but ultimately too easy and short to be enjoyable.
The AI, unfortunately, is still fairly mediocre. Your allies tend to run around aimlessly for a few seconds every once in a while. Same happens for enemy PCs.
Speaking of which, there is PvP in this game, but it's very limited. Either you engage in PvP in the Arena or you find a "PvP encounter" out in the world, in which there is a PK and a person being PK'd, and your goal is to save the person being PK'd. Unfortunately, you can't engage in world PvP against groups of enemies, making PvP very easy there. PvP in the arena can be fairly difficult - 3v3 matches where you cannot use items and where healing spells do 1/2 the effect.
The storyline is not the greatest; it definitely seems like they intentionally made it slow in order to make a long game and/or so that they could make 3 games out of it. However, at the same time, those who have watched the .hack//Roots anime series will get a lot more out of the story than those who have not (those who haven't will likely be confused, as there are a lot of references to events and characters from Roots). It is, though, a very interesting story, with plenty of intrigue. The end of the game definitely leaves you drooling for the next game.
The graphics are *incredible*. Despite a couple slowdowns here-and-there, everything runs smoothly with a great semi-cell-shading look to the game. My only gripe with the graphics is that there is no mouth movement in many of the cutscenes (although the developers did a very clever job of covering the players' mouths with from-behind camera views or their armor for a lot of them).
Voiceovers are surprisingly well-done. Haseo's voice is usually right-on, which was the most important for me. There are a few voices that annoy me, such as Atoli's, which is way too high-pitched, but it's liveable. The fact that Sakaki's voice actor is the same as the person who did Alucard in the Hellsing anime series was awesome... it worked perfectly.
The entire game clocks in at around 24 hours for the main quest plus most of the sidequests. This is a huge improvement over the original .hack series' play time of ~15 hours per game.
I would definitely suggest that any fan of RPGs get this game, especially if you enjoyed the original .hack series at all.