Battling Lasciel for control as she tries to get word to Nick...
I'd read it.
Nah, we've already read about 3 books where the main theme is battling Lasciel for control.
Going with the Darkhallow would have been a harder choice to write, because it's virtually impossible to keep the audience rooting for a character who's life-drained thousands to tens of thousands of people to fuel his own power. There's no reason Harry couldn't have gone on to use that power against N-fected Maeve and then Nicodemus, but a Darkhallow probably would have left him overpowered for those to even be interesting adversaries.
I disagree, you do what you have to do, and Harry always does. I'd still root for him; there's something captivating about someone who's dedicated enough to kill thousands to protect even more. Peace loving ideas aside, historically speaking, to get anything done you have to spill blood, and much of it (even innocent's blood)
I agree with the overpowered bit though.