All of the above! :D
But the storyline is to die for. So well-written. And of course the cinematography is perfect.

Realising Hannibal is a really messed up dude but not wanting him to die? And of course, the chemistry between the two main characters! I love not knowing whether Hannibal is playing Will, or if Will is playing Hannibal? The final episode of each season so far had me sitting at the edge of my seat! The scene, the music, ... the elegance of it all! Visually stunning! Just love this show so much~

Well, all of it, but without compelling characters I'd be disinterested in ships and (typically) storylines that the characters are engaged in. The way Will and Hannibal, for example, are portrayed in the show causes me to ship them (and I do appreciate while their relationship is a central theme, it's not the sole one, and it makes sure to dedicate lots of time building up the characters apart as well as together.

I certainly don't ship them in say, The Red Dragon film, primarily because they're written differently (putting aside that, unlike in the show, it's not even close to being a canon romance in the film).

All of the characters in this show intrigue the hell out of me (especially Will but the others aren't far behind).