Same as the first with minor differences.
.hack/Mutation is actually Part 2 out of total 4 games. The story continued exactly where it stopped in Part 1. Since it is basically the same game as Part 1 so there is not much changes in the gameplay and thus not as excited as the first game.
However, this game also has improved from Part 1 by adding new town & stage, new characters, new weapons & armors, new monsters and new mini game (you can feed some pets and see what are they growing into, and use them for racing). All this has made the game much better than Part 1 and don't forget that the most important part is to know how the story goes. Of course the story progress further in Part 2 but no ending yet.
This game is like an internet multi-player game where you can go everywhere as you like and meet with others players online. You can ask them to join your party or they will ask to join your party to have an adventure together. It is really fun and unique. The graphic and sound are almost the same as Part 1 with minor improvement perhaps.
I cannot recommend this game along because you have to start playing from Part 1 in order to understand everything and you can transfer you save data from Part 1 to Part 2 and then Part 2 to part 3. So I recommend that you try Part 1 first before you play Part 2 for your own advantage.