Good mole in Brooklyn?
I kind of hate to say it because it's 1) expensive and 2) in one of those rotten condo towers, but Mole in Williamsburg (a branch of Mole in Manhattan) really does have excellent mole poblano.
This is just our local place we go to when we want simple food, but Acapulco in Greenpoint has surprisingly good and inexpensive mole poblano. I would not call it a holy grail, but it's good.
The best mole of all time, I am told, was at Bean in Williamsburg, now defunct.