It's an awesome seinen. It's like an ecchi take on some themes from "NHK", a bit more pervy stuff, but more light-hearted... Takes a smutty out-of-body fantasy premise and injects some emotion and mystery into it. And even somehow pulls off a half-decent rush ending.
The way you simultaneously empathize with AND laugh at the slightly creepy nice guy protagonist when he stumbles upon some stuff that begs for brain bleach is priceless... mangaka manages to pull off some twisted crap without being sadistic, either, which is refreshingly delicious.
Also, it's nice to not have a black&white world for a change. The protagonist is a bit of a stalkerish perv and selfish, but has a bit of a heart of gold as well. The antagonists and 'negative' characters are pretty human too, and not just outright utter bastards.
Btw, that "Group Intercourse" tag? MISLEADING... contains 2 incidents related to group sex, neither depicted: one is alluded to and supposedly something the MC witnesses, but all we get is his freaked-out expression and some pornographic sound bubbles from offscreen; and the other is a "spirit orgy" of sorts, but their way of doing it is by overlapping each other's bodies (fully clothed) and getting off on that. In other words: NO GROUP SEX SCENES HERE. No mind break in the hentai sense, either.
Unfortunately, the main mystery is still left hanging :_((