Some spoilers, not specifics, don't wanna put a spoiler tag at every second word, so, warning.
.
.
.
.
.
.
Loved it, a very good anime imho that also abstains from using too many tropes. My main gripe is the main adversary... nuh, I think villain is actually justified... that appears later on. Reminded me a lot of Death Note's L and M, only this time as a villain (yeah, the main characters are the "terrorists", so go figure... ^^).
Every character is more or less realistic, as far as anime goes, at least when it comes to looks. The main characters are geniuses, their main adversary in the japanese police is also highly intelligent, the only one amongst a group of morons apparently. But the main adversary of course dons a sorta-goth-lolita look with huge white hair and OBVIOUS psycho tendencies, which no one in the police and FBI seems to worry about.
Also, the very unrealistic (or not? no clue, seemed like it to me) interaction between the FBI and the japanese police, i.e., the japanese police lets the FBI walk all over them and doesn't even stop the cooperation when the FBI commits plenty straight-up illegal and dangerous stuff.
Those are my two main gripes, otherwise an anime that's rather light on tropes, has a more adult, darker theme and tone, and somewhat morally ambigious.