I have never played the other games, only started recently with BG1 but finding a lot of things irritating about it. I like the openness of this game much better in that there are many paths to take. I don't think we are just an accident, there will be something revealed later on that will show why we are "special". Perhaps there should be hints at this for the impatient people?
The hints are there, but it's an old game and they are quite subtle compared to what you get nowadays. In one particular case the only way to get a companion to spill the beans is to charm them before you talk to them.
Though imo the best game based on the idea of a "mysterious past" you need to uncover remains Planescape Torment.