I absolutely love it. I was reading Asimov's robot novels around the same time I first watched Big O during one of its Adult Swim runs. A certain episode obliquely references the robot novels and I was overjoyed at the coincidence and simultaneity.
I appreciate Big O's ability to tread the line between "case of the week" and the overarching plot. It's one series I wish got just a bit more episodes to breathe.