A great game, closing with a shiny golden key this magnificent .hack trilogy.
There are a couple things than i thought that could be better, however. For example, it was announced that the Azure Knights and Shino would join you, however, this only happens after finishing the game, and that should be different, because that's not when they're useful and the story could be even better if they came before.
As for Patty, you need to enter the Forest of Pain, which can only be done if you did the abyss quest. Which means if you didn't do it in the the Rebirth and want Patty in the party, you have to do it in Rebirth, and do the vol. 2 and 3 all over again. I think ther should have been some message that told that if you did that quest, you'd gain bonuses in the following games. Or they should at least let us do the quest in this game...
Aside from that, it's a must have, however, you should really play the the other volumes (even though i didn't play the original .hack games, i understood the story well and really liked it)