I know that BG has not been TB however I think that this is not what made it a BG game. I have said and I will always say that BG is about the story. To me this has always been what brought me back so many times to replay the game. Each time finding new ways to play and exploring how different parties and actions effect the story. One of the key features of D&D is the ability to tell a story with your friends. In my experience I found it very difficult to play BG1 and BG2 with my friends. I think that this was one of the major flaws of the BG series. A typical attempt would end up in people wandering off around the map, starting combat and dying before anyone could get to them.
I understand that multiplayer in BG could be very effective with the right players. However I have run into constant issues of people not being ready or casting there spells on the wrong person. I think that having TB combat will change the way that we can play this game by enabling awesome multiplayer moments. which, in my opinion is what D&D is all about.
