The conclusion to the cliffhanger.
Nearly everything about the second game is presented in the same way as it was in the first game.
The menus and the mantra grid have gotten minor graphical facelifts and the music is, in my opinion better in this game than the first but overall the system is exactly the same.
A few new abilities have been scattered about the grid and attatched to various Mantras which you'll have to learn all over again. You may load a clear save file from DDS1 that add a few new features and items to the second game depending on the dialogue choices you made and how many optional bosses you've fought.
The new Mantra Grid now resembles one big honeycomb if you will. Learning a mantra unlocks all its surrounding mantras. You're no longer required to work your way down a long line, you can move around and there's more freedom to customize your characters differently.
Which is something that you'll need to do if you plan to succeed in this game. Digital Devil Saga 2 is very, very short. With only 7 different dungeons, one of which you'll go through twice and these Mantras are very expensive. If you try to have every character learn every ability you're going to have trouble if you haven't resigned yourself to hours of leveling in one area.
While this sequel is light on dungeons it is heavy on story, sort of a reverse of the first game. The story of DDS expands in ways that can only be described as amazing. If you relished every opportunity for a story expanding cutscene in the first game then you're going to love this one.
All in all, Digital Devil Saga 2 rather than being a huge stand-alone experience brings an appropriate conclusion to the Avatar Tuner story. So rather than think of them both as independant games they are both more like two parts of a whole. If you're a SMT fan then I highly reccomend both of them to you.