I was very satisfied with the expansion of Shadows of Amn. It provides plenty of new options for experienced players and finishes out the story in a great way. I expect it'll be sucking up a lot of my free time in the next few months.
My only big problem (and this was something I had to deal with in the last game too) is that it has some pretty annoying bugs, specifically one in which your characters' pathfinding AI breaks down and they can't walk around any obstacles. Whenever this happens, I have to eject the game and restart my computer, this is the only thing I've tried that is guaranteed to make this go away.
Even though it tends to make my gaming experience more frustrating, don't let that stop you from buying this title, in my opinion it's the best part of an incredible series.