Dorothy is a foreign exchange student, as well as the protagonist's new maid and his fiance (sort of). To be blunt, I dislike her character so much outside of her route that I wanted to smash her head in with a steel rod. Nonetheless, her route was actually pretty good. I was surprised at how good it was. I cried for it almost as much as I did for Michiru's, if for different reasons. If you can stand her, this is an excellent route to choose.
Kuro is the female version of the god of time, Chronos, who is connected to the protagonist's watch. She is one of the game's two resident lolis (who are incidentally the true heroines *laughs dryly*). Her route is the most out there (fantasy), in terms of overall content, and it shows off the best of the protagonist as well (though Michiru's route also shows off his good qualities). Kuro is also really adorable as a heroine, and her personality changes a lot as a result of the events in the route. I will say that the actual progress of the route is rather predictable... so predictable that I was reminded of a Key nakige route.
Miu is a clumsy genius with horrible luck (to a ridiculous degree at times). She is honest, kind-hearted, and also brilliant... she is also the focus of the first half of the common route, so most of the development leading up to her ending occurs there. As a result, her 'ending' really is only an ending that you get by going back to the first choice. That it is heart-warming is because of how all the events in the story are connected. Along with Kuro, she is one of the two seemingly 'true' heroines (to be honest, calling them true heroines is probably inaccurate in this case).
My final thoughts on this game are... that it is nowhere near Hapymaher or Mirai Nostalgia in terms of impact or quality, but for those who wanted a generally heart-warming story about personal growth with some fantasy mixed in, it is actually an excellent choice. For those who hate explicit sexual content, it is also a good choice because the H-scenes are set aside in a corner where you don't actually have to read them.