at first, it goes through same old same old path other harem manga takes. introduce the girls, some conflicts, some misunderstandings, etc, etc. everything is fine and dandy and they are all so cute, with the main character the usual kind hearted, follow along with anything kind of guy that populated the harem world.
then it goes overdrive to sex mode. all the orgasmic expression, the foreplay, the boobs...well, the mangaka draw hentai, so it's not that bad. however, one cannot really get into it because the mangaka love to super impose cute on sexy, and you just end up laughing seeing the cherubic, round and cute face of Nagi sucking on a girl's boob. i was quite perplex with the choice of character design at such point in story, but i chalk it up to the mangaka trying to keep the tone as low as possible and dont become full on hentai, though it feels a bit shotacon and lolicon ish.
then towards the end everything goes dark, the characters become dark and theres some unbelievable sex scene (the last one). with so much flashback and supernatural happenings, you know things finally getting serious.
but then it goes happy ending at the end so everything is fine, and you are fine. you just have this niggling question - wheres the sequel because you really want to see how are their kids holding on.