Do not take the GameSpot review for face value...
As for major changes to the series from the first series to the G.U. series:
1: Improved Graphics. The in-game graphics in this game look better than some of the better cut scenes of the last series.
2: Improved Controls: The controls are much easier to use when it comes to using a weapon skill now than they were in the previous series. You also have to use a little timing for your attack combos, instead of the mindless button mashing the last series was infamous for.
3: Improved AI: your teammates in this game no longer feel like dead-weight when you don't give them a command. They usually attack the closest target, activating weapons skills on their own, without telling them to. If you want them to use a certain skill, you can still go into the menu and select the skill and target, like in the last game series. The enemies are also a little better than they were in the last series... especially the ones whom represent 'players' like the PK's, Doppleganger, etc.
4: Improved Storyline: Cutting out the seemingly pointless missions from the last series and combining the four volumes together, the total storyline length is about the length of Volume1 and 2/3 of volume2 when you do the same to them. Plus side, no going through random dungeons aimlessly just go get an email from someone telling you to go to another pointless dungeon. It's pretty much straight forward, with the 'memoir' option to recap what's happened so far and where you still need to do. Final note on this topic, believe it or not, you do NOT have to play the first series to enjoy the new one. Knowing the extra information is nice, but it doesn't do much to help understand the new plot.
I believe that is the best way to not only describe this game, but how to separate it from the last series. Spoiler... the final storyline boss in this game is a PAIN to beat. Better be in the later 80's early 90's level wise if you want to kill him.
Depending on weather or not you played the first volume of the G.U. series, the learning curve can be either 0-30 minutes, to 30-60 minutes.