It may not be much different than the first, but it's great game for fans of the series.
The story continues straight after the first installment. Kite defeated Skeith, which caused the birth of the giant monster Cubia, Kite and BlackRose continue to divulge into the mysteries of "The World", going as far as working for the system admin, Lios. Eventually, you get to go to Net Slum, home to the infamous hacker, Helba, and fight another Phase like Skeith (the game pits you against the next two), which in the end causes a nice little plot twist.
The gameplay is still repetitive and unfortunately, like the first game, doesn't have much variety. The game still keeps the strategy from the first one and you will find yourself using elemental advantages as the only advantage and getting annoyed by enemies with tolerances to certain elements or attack types (physical or magical). A cool new feature called Grunty Racing is added, though. It's basically racing around servers with the Grunties you raised (there are three types to a server) capturing flags in a certain time to get cool items, including Images for getting first.
This game also comes back with more easter eggs, this time expanding beyond the simple images and music. Now, you can see scenes from .hack//SIGN word-by-word. There is a little side effect, though, as the scenes are water-down to fit the graphics of the game.
Data Flag also returns, with the ability to start a file with your character from the first game and save another Data Flag after beating this one. It is highly recommended to use the Data Flag, as the game is meant to be played that way and you will end up facing lots of high-leveled enemies of you don't.
Despite it's minor flaws, the game is just as good as the first, with characters and a plot that doesn't disappoint, which is what RPG's are made for.