I think cosplays from Hannibal are something that would require the cosplayer to really act in character in order to get the message across. So someone cosplaying as Hannibal would have to replicate Mads Mikkelsen's accent and voice almost perfectly and replicate Hugh Dancy's speech patterns that he uses as Will. I also think whoever cosplays these people would have to look a fair amount like them (or at least they'd have to be able to do makeup to look a fair amount like them) to make the cosplays work.
You could also incorporate some clever props with your cosplays too to get the message across. I think these cosplays would wonderfully as a photoshoot setup rather than for wandering around the convention. It would be pretty damn awesome if some cosplay group replicated one of the crime scenes in the show and used that for their photohsoot set.