BG1 follows the story of the young and reckless Bhaalspawn. It ends with the death of your “brother” Sarevok. The whole time you are trying to just figure this out and understand why he wants you dead.
BG2 you have been robbed of your possessions and experimented on. You know what you are but not why you are. While avoiding Irenicus and building back your character you discover the Slayer and more about the God that made you.
BG3 you are the helpless victim of mind flayers. You have formed a weak and compromised party that shares your fate and end goal. You know that Baldurs Gate is near but still out of your way and you know that at any moment you die and a monster will take your place.
The first two do share a central theme, Bhaal. However the game is not flushed out and you do not know what forces and characters are behind your fate and what your character is in the grand scheme of things...
