Well, personally I also don't think BD is that bad. It's not as good as DD (but I also find that game to be amazingly good) but I had some fun playing through BD. I also didn't have that big a problem with the deathknights voice, but that could be because I'm not a native english speaker myself (which should be evident from this post I guess
As someone already mentioned Larian wanted to try out some new things, both regarding game design but also the technical angle to developing RPGs.
I have to mention that I'm not a developer at Larian, so the things I describe in the next paragraph is what I remember from their forums (which I visited a lot around the time when BD came out). Anyway, since I'm a programmer I'll describe the new things they wanted to try out in the technical department first. They recognized from their experiences with DD that developing a completely open game like DD was very very hard, and many bugs arised because the quests could be done in many different orders and different manners etc. So with BD they wanted to try and develop a much more linear game, which they split into 4 "acts", where each act is *completely* seperated from the previous ones. You can almost think of each act in BD as a seperate game. The (at least theoretical) benefit from this approach was that they could test and develop each act completely seperate from the other ones. Now, to make this work as a full game they just had to develop some system to transfer the two main characters and their equipment from one act to the next - but unfortunately they ended up having many bugs in *this* system
This shows (or showed, don't know if they fixed all the problems yet) up as problems such as items loosing their stats when going between the acts etc.
They also changed a lot from DD in the game design - such as introducing the party-based gameplay, developing a completely new skill system etc. The main idea in the new skill system is that you can (again in theory) "shape" or "create" your own skills, by building them from a tree system. Whether you like these changes is a matter of personal taste I guess. Personally I agree with most other players that the system in DD was much better. On the other hand I don't really have a problem with games being linear, or even dungeon crawls - as long as the game is interesting I don't care if its an open or linear game experience. In the case of BD I just ended up missing the lush and green outside world that DD provided. BD takes place almost exclusively in dungeons, caves or dark alien worlds. Again, it's a matter of personal taste. BD *did* have some interesting moments and nice puzzles though!
Whether to recommend the game or not? That's hard to say. If you liked DD and can get your hands on BD I think you should try it out and make your own opinion of the game..
PS. Sorry for the length of this post