The ending is essenitally the same for all characters, regardless of their alignments and/or their in-game actions. In the original campaign you still have to defeat Morag. In SoU you have to beat Heurodis. In HotU, you have many options regarding the fate of Mephistopheles. You can destroy him, fight him(and either defeat him or die trying, lol) or replace him as the ruler of Toril (not sure on this one. Moderators, please correct me if I'm wrong.)
There are no "punishments for evil in-game deeds. This is what I personally find repulsive in the game.
