I started reading this today and I have to say that I am expecting great things from it.
The manga seems to have all the right items in place in order to have a wonderful story. It helps that I can't immediately predict how the characters are going to act for the rest of the manga (I find I can do that with allot of them)
The artwork is pretty good. Nothing outstanding but not bad either.
The story is the main selling point for me so far. It starts off pretty dark and with an extreme element of supernatural which immediately draws me in.
The characters are
great as well. You have your funny perverted guy friends, your attractive and secret admiring female school mates, crazy and crazy hot sister, and a pair of protagonists who I am very much looking forward to finding more about!
So for the ecchi factor. I think I am going to develop a scale of 1-10. 1 Being PG and 10 being Full blown Hentai. This manga seems to fall around a 6.5. Not that I consider this an inherently bad thing mind you ; ). If any of the other mangas I have read in my life are any indication though, Mangakas seem to start off somewhat slow then rev up the ecchi engine later in the series when they get braver. We shall have to see.
All in all the story had me at around chapter 2 and I will now be looking forward to staying up to date and reading more!