Neverwinter Nights 2 + Mask of the Betrayer Reviews has reviewed both the original Neverwinter Nights 2 and its recent expansion pack, Mask of the Betrayer. A snip from the former:
One thing that was done differently in the original Neverwinter Nights from earlier titles, was not utilizing proper group of adventurers as one would in the D&D universe. That is to say, everything focused on controlling a single character rather than managing a party. This worked well for the way the game played, but I assume that the designers decided to change this design in this newer game. Obsidian gives you full control of the party, which can vary in size depending on the part of the game. From leveling up the character to selecting which spells or abilities they will use, the player has the option to control the details, although they aren't required to micromanage unless they want to.

And a snip from the latter:
The gist of the plot is that no matter what class or race you play, you remain the character from the original campaign. This means that having the experience of the first part will give you a little more understanding as to why you are there, though it isn't required for more than exposition and back story. Your character wakes up in a mystical "cell" in a cave, and the fancy silver shard that was the focus of the original campaign has been removed from your chest. This opens a sense of hunger in your character that, as you progress, develops into a soul-eating addiction. Now, that sounds a little strange, but I'll go into more depth a bit later.

Again, it is difficult to go too far in depth on the plot without ruining some of the joy of this game, but in general, you are trying to find out what happened to put you in this situation in this somewhat far-off part of the world. The other Neverwinter Nights titles took place primarily in the Sword Coast area of Faerun, but the designers have moved on from this area of the world and set this chapter in the far-off Rashemen. This setting ties in nicely to the focus of spirits and souls as the land is full of them.