Easily the best story I've played with in a CRPG.I really do have to say that thieves were all but useless. Personally I went with a mage, and switched to fighter periodically so I could increase my slots of Dagger.
The game is just so rich in its settings and plot that I was captivated pretty much from the start. It was also very cool that the NPCs in your party were actually important parts of the story instead of Hit Point Blotters and Mules like in most of the BG Games.
Granted the BG games had sidequests for the various NPCs, and I'm not knocking the games at all - I love them. I play BG2 all the time, replay it, try new character combos...very addictive.
BUT -- PS:T plain and simply has the better story line.