Stiles is perfectly believable and sympathetic as a rape victim, but taking that extra step to being a crazed and obsessed vigilante just doesn't seem like something she could ever be capable of.
I agree. She's not delivering the idea that there's a surpressed psychotic edge to her.
The story is okay, I guess, but it would be so much better if a) Dexter were unravelling because of Rita's murder (he barely even seems to remember it now) and b) Lumen seemed like much more of a loose cannon, which Dexter was too wrapped up in his own psychosis to notice or care about. They should be like the Macbeths, two people who are more dangerous together than in isolation because they magnify each other's evil. We should be terrified for them, and terrified what they might do next.
I'm wondering if all the actual rapists will be killed by mid-season and then Lumen decides she's not going to stop, and starts killing any guy she decides is a rapist, which of course could be anyone. Then what does Dexter do? Maybe at that point, the story will kick back up to the level we expect from this show.
But to be fair, it would be hard for a LOT of actresses to pull that off. You'd almost need someone who already has quite a bit of an edge to her, like a Michelle Rodriguez.
Or a female Michael C. Hall.
I guess this is a lesson in how rare actors like that really are because Julia Stiles is hardly untalented.