Mmmk...This manga is either really good or just above average, I can't tell.
It's safely good [7/10-ish], as even if you just skim it it's got the epic scaffold of a guy watching a girl who, every night, fights a chainsaw-wielding, black cloaked man, temporarily getting physical superpowers during the fight. (At least I don't think she has them during other times) It's got that kinda cliche, exploitation that everyone loves with a title to match like the idea behind 'Hobo With A Shotgun' <--- It's a HOBO with a SHOTGUN.
Now, the question is, is it great when you look deeper (e.g. Penguindrum) or does it fail horribly in that respect like some amateurish 'deep' stuff out there (e.g. the limbo scene in Harry Potter's 7th book, {Basset fans are scary, so I won't manage that})?
I...have no idea. I think looking a little deeper at least gives it 1 more out of 10. But I didn't really like any of the characters. No, that's wrong. I'm interested in at least the dead friend and the final chapter where the guy (you'll know who when you read it) is talking. But I don't think the characterisation overall was done competently.
Perhaps I want this to be a 10/10 because it's the author of Welcome to the NHK! who managed to make me feel depressed for days after just reading a few chapters from the beginning and end.
Bottom line: Despite whatever makes this good, the characterisation was bad and the romance was bad.
EDIT: Art was pretty great. especially cover art.
I think the live-action version of this could be done really well, depending on how they approach (I'm thinking Kill-Bill-esque) but I don't think I'll bother checking it out 😛