I'm on the 10th episode of The Big O. It's funny, but the series feels more distinctly American than any anime I've seen. It has more in common with detective/noir films than with your typical mecha fare. This is evident in the tropes/archetypes that it follows. For one thing, the main character is NOT an effete, brooding teenager. Rather, we have a very gentlemanly, very laid-back, very LIKEABLE bachelor in his late 30s by the name of Roger Smith, who lives by various idiosyncratic rules, like "the good guys must always wear black".
We also have a typical English Butler,
a Tough Cop with a Heart of Gold,
and a Femme Fatale....
again, more Western/Noir tropes. The music (jazz/blues) adds to that effect.
But my favorite character of the series is R. Dorothy Wayneright. An android whose intricate construction allows her to pass for human at first glance, she ends up working as Roger's maid. However, she isn't a subservient blob of moe. She's sarcastic, witty, and completely unafraid to make fun of all the other character's antics. Also she can punch through your neck and rip out your spine.
fun fact: sunrise studios (the animators for big o) were subcontractors for batman: the animated series (the 90s one)... no wonder they look so familiar