Baldur's Gate II: Shadows of Amn (SoA) is in lack of a better word perfect. It has the perfect story, it has the perfect characters who are developed better than character any other game.
First of as previously stated the story is perfect. It is quite non-linear like the first game was but after a certain point it becomes quite linear which also suits it because the linear part of the game is so well done. Furthermore depending on your character you can now grow romantic attachments to certain members of the party which is a very fine addition to the character development which is already considerable. You get a far greater hatred for the villain, Irenicus, who is by far the most interesting villain ever in any game.
Another thing that works perfectly in this game is the voice-acting which is the best voice acting in any game prior to SoA. Especially David Warner who provides the voice for Irenicus is brilliant and really gives both edge and depth to his character.
The gameplay is similar to the previous game and is therefore quite straight forward if you played the first Baldur's Gate game. If you have not however then there is a very good introduction to the game where the basics are explained in a way that is easy to learn.
All in all Baldur's Gate II is the best game ever made with immense storyline, great character development and fun gameplay for many hours