No pun intended - I assume you have seen at least the first Diabolik movie (the predecessor for this that is and not the Mario Bava movie from the 60s). With that in mind, all major returning characters are being played by the same actors ... except the one that should matter the most: Diabolik ... it is a different actor altogether! For whatever reason (I did not check for the reason to be honest) ... I won't speculate.
What I can say is that this does not fair as good as the first movie. I can only hope that part 3 ramps things up a bit ... maybe with another Diabolik actor? I would not really be surprised. We get some new characters and actors added - mainly Monica Belucci - if you know her, you probably love or loved her at one time. She still has the charisma - but some people who criticize the movie say she is not close to the characters she is supposed to portray ... something I can't confirm or deny, since I have not read any of the comic books (graphic novels) ... not the best throwback ever (go to the original), but not the worst either.