Arika's path is... one of the ecchi-est paths I've seen in a non-nukige in a while.  That is to say, Arika plays the role of the 'honor student' of the future, the ideal of the people from Yoshikazu's era.  There are minor spoilers in the box below, but they were significant enough I had to box them up. 

Until she comes to the village, she has no doubts that the rules she lived by were correct and proper... in fact, it never occurred to her to have doubts.  She thought romantic love was an anachronism and that sex was just a barbaric element of humanity's path... that is until a certain event in the common route that pretty much reverses that viewpoint.  Unfortunately - or fortunately depending on how you look at it - she also has none of the cultural 'baggage' the average young person today has when they consider love, sex, children, and marriage.  That is what makes her path so interesting, because they basically put a 'true innocent' into a situation where she learned about all this without any of the extraneous bits of understanding that come from watching and imitating the adults around her. 

Besides this, it addresses seriously a number of issues when it comes to modern child-rearing and the reasons why it has become so hard (in an oblique manner) for kids to be raised in an era where most people live urban lives.  Overall, it is an excellent path, even if it is one that makes you want to run for the toilet in a good way. 

Kotobuki's route comes at some of the same issues as Arika's from another point of view.  Kotobuki suffers from a typical malaise common to some young women, where the idea of sex in general seems unclean or wrong to them.  This is reflected in their reactions to the opposite sex in general, and they often overreact by coming to prefer extremely concealing clothing. 

In Kotobuki's case, as she grows to love the protagonist and after they become lovers, she slowly eases aside the distaste she felt, growing beyond her instinctive categorical denial of the acts of love and sex. 

This is the first time in the VN that you really come across the difficulties of the divide between the past and future, for the simple reason that the protagonist and heroine are on opposite sides.  Yes, it is an issue, both throughout the relationship itself and during its formative stages.  I think they did a really good job of bringing Kotobuki to life during this route, giving her feelings significant impact, when matched to the protagonist's own.   While Kotobuki herself fits into the classic 'yamato nadeshiko' archetype, she also shows a great deal of growth in the story, and that is one of the primary reasons I liked this path so much.  

Iroha... Iroha is pretty much the picture of the 'innocent girl' heroine.  She is one of those girls who speaks of herself in the third-person, and she is unbelievably 'genki', always smiling, always having fun, always affectionate, like a puppy.  This doesn't change much throughout the path, though the 'flavoring' of her outlook on life does change somewhat after she and the protagonist become lovers.  Unlike the other three paths, there is a rather significant obstacle to overcome in their case (or rather, it wasn't resolved in quite as simple a way).  Overall, I found her path enjoyable, though I - quite honestly - enjoyed the other paths more, if only because I liked their epilogues more (I really wanted to see a five-years-later Iroha). 

Overall, this VN definitely meets my standards for a first-rate charage, and if you do enjoy that kind of thing, this is an excellent choice.  It is also a solid VN of the Month candidate, and it is always nice to have more of those.  It is a highly ecchi VN, and it also contains quite a bit of propaganda.  However, the propaganda isn't overbearing and it is subtle enough that it doesn't destroy the atmosphere at all most of the time (in fact, it is part of the atmosphere lol).