Big O is not like any other show I have ever seen. The writers clearly have extensive knowledge concerning Greek mythology and even Christianity. It is a cartoon sure, but the depth of the show is very subjective. The show itself gives the viewer just enough clues to allow one to believe that all of the other unending parade of questions will somehow be answered, but apparently, they won't. The show walks a profound balance of story and probability and divine vagueness.
I saw a few episodes of this show and became hooked like no other show I have ever seen. The overall themes are far from light. Two of them being memories and ultimately attempting to define life. What is the value of one's life without memories? What separates humans from androids in a futurist world without knowing which actually came first? And that is assuming who and what each character actually is, which is far from a given. My obsession with the show did eventually wane, largely because the show itself is rather slow at times. There are plenty of action scenes with enormous robots, also representing something I'm sure, to balance the pace, but those battles rarely excited me.
The truly strange aspect of this show is that the majority of it for me is window dressing. It's the symbolism that is scattered throughout each episode that elevates this show to atmospheric levels. This show is just smart enough and just open ended enough for each little mysterious detail to have some profound meaning. This show has everything within it to be the basis of a new religion in and of itself, seriously. The fact that all the answers can plausibly be answered, but aren't, makes Big O that much more life-like in nature.